SRF2013 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOIOA03	The Challenge and Realization of the Cavity Production and Treatment in Industry for the European XFEL	cavity, controls, superconductivity, HOM	18
	W. Singer, J. Iversen, A. Matheisen, H. Weise DESY, Hamburg, Germany P. Michelato INFN/LASA, Segrate (MI), Italy
	The main effort in production of 1.3 GHz cavities for the EXFEL was dedicated to transfer the superconducting technology to the industry. These know how transfer is executed by DESY and INFN/LASA team. The preparation phase based on prototype cavities covered: qualification of potential vendors for material and cavity fabrication; work out recipe and strategy for qualification of the infrastructure for cavity surface treatment at industry; definition of the quality management strategy, documentation and electronically data exchange. Production of 800 series cavities on the principle “build to print” is contracted to companies Research Instruments and Ettore Zanon. High purity niobium and NbTi for resonators provides DESY. The principles of the material and cavities production in conformity with European Pressure Equipment Directive are developed together with the notified body. New or upgraded infrastructure has been established at both companies. The first several tens of series cavities have been produced and treated. Most of the cavities handed over to DESY up to now fulfill immediately the EXFEL specifications. The cavity production for EXFEL will be finished mid of 2015.
	Slides MOIOA03 [7.394 MB]

MOIOC01	Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities	cavity, interface, coupling, operation	57
	V. Palmieri INFN/LNL, Legnaro (PD), Italy
	Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.
	Slides MOIOC01 [15.558 MB]

MOIOC02	A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor	cavity, impedance, electron, superconductivity	63
	B. P. Xiao, C.E. Reece JLab, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: This manuscript has been authored in part by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. There is a need to understand the intrinsic limit of RF surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors, based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and Fermi Lab with carefully prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.
	Slides MOIOC02 [3.122 MB]

MOP032	Statistic to Eddy-Current Scanning of Niobium Sheets for European XFEL	cavity, controls, survey, superconducting-RF	171
	A. Brinkmann, S. Arnold, A. Ermakov, J. Iversen, M. Lengkeit, A. Poerschmann, L. Schaefer, W. Singer, X. Singer DESY, Hamburg, Germany
	The fabrication experiences of superconducting cavities for FLASH have shown that eddy-current scanning of the Nb-sheets foreseen for half-cells reduces the cavity failures. New eddy current devices have been developed and build together with the industry for the production of 800 pieces 1.3 GHz superconducting niobium cavities for European XFEL. More than 15.000 Nb-sheets provided by three companies have been tested by eddy-current scanning. The sheets that demonstrated local deviations of the signal have been subsequently non-destructively examined by 3d-microscope and X-Ray element analysis. The surface defects (dents, holes, scratches) are the mainly detected flaws. In addition several types of foreign material inclusions observed. Statistic concerning eddy-current signal deviation and rejection rates for each supplier will be presented.

MOP033	Quality Assurance and Acceptance Testing of Niobium Material for Use in the Construction of the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU)	cavity, linac, SRF, controls	174
	C. Compton, D. Miller FRIB, East Lansing, USA T.R. Bieler, D. Kang Michigan State University, East Lansing, USA S.K. Chandrasekaran, N.T. Wright MSU, East Lansing, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University Niobium is the current material of choice for the fabrication of superconducting radio frequency (SRF) cavities used in SRF based accelerators. Although niobium specifications for this application have been well established, material properties of as-received materials can still vary substantially. As required for the FRIB accelerator, large volumes (60,000 lbs) of niobium materials (sheet, tube, and flange) have been contracted to several niobium vendors. The FRIB cavity designs require very large niobium sheets, increasing the difficulty in fabrication and potential for contamination. FRIB has developed and initiated plans to control niobium specifications and perform incoming acceptance checks to ensure quality is maintained. Acceptance results from the first niobium shipment will be presented, looking at several production lots from the same vendor and across multiple vendors. Non-conforming results were observed and will be discussed including follow-up investigations and mitigation strategies to improve quality of future shipments.

MOP034	The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON	cavity, target, controls, accelerating-gradient	180
	A. Gresele, M. Giaretta, A. Visentin Ettore Zanon S.p.A., Nuclear Division, Schio, Italy A.A. Sulimov, J.H. Thie DESY, Hamburg, Germany
	Serial production of superconducting cavities for European-XFEL was successfully started at E.ZANON at the end of last year. The production rate (3-4 cavities a week) allows us to summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed. The last results of new preparation cycles development in the frame of E-XFEL projects is also included

MOP035	Using an Engineering Data Management System for Series Cavity Production for the European XFEL	cavity, controls, database, data-management	183
	J. Iversen, A. Brinkmann, J.A. Dammann, A. Poerschmann, W. Singer, J.H. Thie DESY, Hamburg, Germany
	For series production of 800 superconducting cavities for the European XFEL an Engineering Data Management System (EDMS) is in use as a tool for quality control and quality assurance. DESY is responsible for “in-time” supply of more than 24000 semi-finished products of niobium and niobium-titanium alloy. The EDMS as a main repository was set up to fulfill logistic requirements and to guarantee traceability and documentation issues according to the European pressure equipment directive (PED 97/23 EC). The main aspects consist of complete paperless documentation, fully automated transfer of quality management documents and data from vendor system to DESY’s EDMS, providing to industry an access to relevant documentation and processing of release procedures for acceptance levels and non-conformity reporting. A summary of documentation methods, procedures and first experiences will be presented.

MOP036	New Technique and Result of Laser Welded SCRF Cavity Developed at RRCAT	cavity, laser, vacuum, experiment	186
	P. Khare, R. Arya, J. Dwivedi, R. Ghosh, G. Gilankar, C. Gupta, P.D. Gupta, A. Jain, S.C. Joshi, G.V. Kane, R. Kaul, P.K. Kush, G. Mundra, S.M. Oak, C.K. Pithawa, P. Ram Sankar, S.B. Roy, V.C. Sahni, R.S. Sandha, P. Shrivastava, B.N. Upadhyay RRCAT, Indore (M.P.), India C.A. Cooper, C.M. Ginsburg, A. Grassellino, C.S. Mishra, A.M. Rowe Fermilab, Batavia, USA
	A new technique to fabricate SCRF cavities with the help of laser welding process has been developed at Raja Ramanna Centre for Advanced Technology RRCAT), Indore, Department of Atomic Energy, India. In this technique, a pulsed Nd:YAG laser has been used and welding was performed in inert gas environment, in a specially designed welding rig. The advantages of this technique are reduced cost, small heat affected zone, no necessity to weld in vacuum and enhanced rate of production. The paper describes the technique and fabrication method of a single-cell 1.3 GHz SCRF cavity which was fabricated at RRCAT with this new technique. It also discusses the test result of this cavity which was processed and tested at Fermilab. The cavity reached an Eacc of 17MV/m with a Q0 of 1.4 E +10 at 2K. The cavity is being barrel polished for further improvement.

MOP038	Series Production of EXFEL 1.3 GHz SRF Cavities at E. Zanon: Management, Infrastructures and Quality Control	cavity, SRF, controls, cryogenics	194
	G. Massaro Ettore Zanon S.p.A., Nuclear Division, Schio, Italy G. Corniani, M. Festa, M. Maule Ettore Zanon S.p.A., Schio, Italy
	In this paper we report on the capability of Ettore Zanon S.p.A. (EZ) to implement a EXFEL 1,3 GHz SRF cavities production system. In order to assure the series efficient repeatability of the product, this system is based on work team, composed of people with different skills, qualified infrastructures and technical procedures. A detailed study of the different work phases of the production cycle has been performed in advance, highlighting the technical difficulties and the production constraints. Based on this result, infrastructures and processes have been optimized to grant the specified quality and time/cost requirements and procedures and operating instructions, where the most complexes and delicate phases as well as the responsibilities and acceptance criteria are investigated, have been introduced. Qualification operations and eight pre-series cavities have proven EZ capability of fulfilling the imposed requirements. The above described manufacturing system allows nowadays a production rate of 4 cavities per week. EZ future developments involve minimizing time and costs while keeping the highest quality standard.

MOP045	Electropolishing for EXFEL Cavities Production at Ettore Zanon SpA	cavity, controls, cathode, superconductivity	220
	M. Rizzi Ettore Zanon S.p.A., Schio, Italy A. Gresele Ettore Zanon S.p.A., Nuclear Division, Schio, Italy A. Matheisen, N. Steinhau Kühl DESY, Hamburg, Germany P. Michelato INFN/LASA, Segrate (MI), Italy
	A new horizontal electropolishing (EP) facility has been implemented by Ettore Zanon SpA for the series production of the EXFEL cavities produced by the company. According to EXFEL specification a bulk EP of at least 100 micron is the first step of the surface treatment for high performances. Particular attention has been dedicated to find the best configuration during qualification of the system. Correlation between process variables, RF tests at room temperature at Zanon and vertical RF tests at 2 K at DESY have been investigated and the Niobium removal optimized. The facility has been designed for industrial scope, in order to guarantee the required quality and production rate of 4 cavities per week. One of the most important aspects has been the system automation to have complete control of the process.

MOP048	PED Requirements Applied to the Cavity and Helium Tank Manufacturing	cavity, linac, controls, operation	227
	A. Schmidt, J. Iversen, A. Matheisen, W. Singer DESY, Hamburg, Germany
	For the European XFEL more than 800 Cavities are manufactured by industrial partners. Each cavity is housed in an individual cryo vessel, the so called helium tank. All vessels are made from titanium and manufactured by industry as well. The cavity, welded into its helium tank, is a pressure loaded part and has to follow the pressure equipment directive - PED (97/23/EC). Setting up a series production of cavities and helium tanks by different vendors according given standards, was the task of the EXFEL WPG-1 LINAC-WP04. In cooperation with the TUEV-Nord as the notified body, DESY is responsible for the qualification of design, material in use and reasonable tests to get a certificate for pressure bearing parts.

MOP062	Production of 500 MHz SRF Modules the KEKB-type for Taiwan Photon Source	SRF, cavity, operation, vacuum	263
	Ch. Wang, L.-H. Chang, M.H. Chang, L.J. Chen, F.-T. Chung, M.-C. Lin, Y.-H. Lin, Z.K. Liu, C.H. Lo, M.H. Tsai, T.-T. Yang, M.-S. Yeh, T.-C. Yu NSRRC, Hsinchu, Taiwan T. Furuya, K. Hara, T. Honma, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Nishiwaki, S. Takano KEK, Ibaraki, Japan F. Inoue, K. Sennyu, T. Yanagisawa MHI, Hiroshima, Japan
	The KEKB-type single-cell 500-MHz superconducting radio frequency (SRF) modules have been selected to power the 3 GeV, 500 mA, storage ring of the constructing Taiwan Photon Source (TPS) at National Synchrotron Radiation Research Center (NSRRC). The design target is to routinely deliver RF forward power up to 300 kW, CW, to single SRF module with highly reliable operation. Three sets of SRF modules have been successfully produced under a tight collaboration with High Energy Accelerator Research Organization (KEK) and Mitsubishi Heavy Industries Ltd. (MHI), after obtaining the technology transfer from KEK. MHI is responsible for the mechanical fabrication and cryo-module assembly, KEK for the surface and RF treatments of the niobium cavities, high power input couplers and HOM dampers and for the liquid-helium tests of the cryo-modules, and NSRRC for the electronic/diagnostic system, final assembly and system integration, high power horizontal test, and reliable test. This work reports the results obtained during the production of these three SRF modules at KEK and NSRRC.

MOP066	Development of Compact Cryomodules Housing HWRs for High-intensity SC CW Linacs	cavity, cryomodule, linac, proton	277
	P.N. Ostroumov, Z.A. Conway, S.M. Gerbick, M. Kedzie, M.P. Kelly, S.H. Kim, S.V. Kutsaev, R.C. Murphy, B. Mustapha, T. Reid ANL, Argonne, USA D. Berkovits Soreq NRC, Yavne, Israel S. Nagaitsev Fermilab, Batavia, USA
	Funding: This work was supported by the U.S. Department of Energy, under Contracts No. DE-AC02-06CH11357, DE-AC02-76CH03000 and ANL WFO No. 85Y47. Acceleration of high-intensity light-ion beams immediately after an RFQ requires a compact accelerating and focusing lattice with a high packing factor. We have developed a cryomodule which satisfies this requirement with eight accelerating-focusing periods for Project X at FNAL. Each focusing period consist of a 162.5-MHz SC HWR, a SC solenoid and a beam position monitor. The highly optimized EM parameters of the cavity were achieved by using double conical, hour glass like, inner and outer conductors. This design is also favorable for the beam dynamics because the short focusing periods which helps to better control the beam quality. All sub-systems of the cryomodule, except the vacuum-vessel, are in advanced stages of prototyping and testing. A similar concept has been developed for the design of several cryomodules for a 20 MeV/u proton/deuteron 200 kW linac at SNRC. These cryomodules house two types of 176 MHz half-wave resonators and require only modest modifications for the application. This paper will discuss the status of the FNAL cryomodule design and sub-system fabrication and its impact on future HWR cryomodule such as the SNRC project.

MOP070	Results on Quality Factors of 1.3 GHz Nine-Cell Cavities at DESY	cavity, factory, operation, linear-collider	297
	F. Schlander IKP, Mainz, Germany F. Schlander DESY, Hamburg, Germany
	Superconducting cavities made of niobium are the basis of many particle accelerators around the world. Besides the quest for high accelerating fields for projects like European XFEL and the International Linear Collider, the quality factor, a measure for the resistance and hence the ohmic losses, is of importance, as it eventually determines the cryoplant size and its costs of operation. Especially for accelerators operating in continuous wave mode, the dynamic heat load generated by cavity operation exceeds the static heat load by far and thus requires minimisation. To investigate the current quality factor performance of 1.3 GHz cavities at DESY, the test results of some 50 recent cavities with state-of-the-art treatment have been examined regarding surface treatment and material.
	Slides MOP070 [0.590 MB]

MOP073	IHEP 1.3 GHz Low Loss Large Grain 9-cell Cavity Fabrication, Processing and Test	cavity, HOM, SRF, vacuum	305
	J.Y. Zhai, J. Gao, S. Jin, Z.Q. Li, Y. Liu, Z.C. Liu, Z.H. Mi, X.H. Peng, T.X. Zhao, H.J. Zheng IHEP, Beijing, People's Republic of China C.A. Cooper, C.M. Ginsburg, T.N. Khabiboulline, A.M. Rowe, D.A. Sergatskov Fermilab, Batavia, USA J.X. Wang, H. Yu, H. Yuan BIAM, Beijing, People's Republic of China
	The combination of the low-loss shape and large grain niobium material is expected to be the possible way to achieve higher gradient and lower cost for ILC 9-cell cavities, and will be essential for the ILC 1 TeV upgrade. As the key component of the “IHEP 1.3 GHz SRF Accelerating Unit Project”, a low-loss shape 9-cell cavity with full end groups using Ningxia large grain niobium (IHEP-02) was fabricated at IHEP in 2012. The cavity was processed (CBP and EP) and tested at FNAL. The cavity processing,test performance and gradient limitation is reported in this paper. We will weld the helium vessel, assemble the magnetic shield and install the cavity to IHEP ILC-TC1 cryomodule.

TUIOA01	Influence of the Couldown at the Transition Temperature on the SRF Cavity Quality Factor	cavity, shielding, SRF, experiment	370
	O. Kugeler, J. Knobloch, J.M. Vogt HZB, Berlin, Germany
	The quality factor Q0 that can be obtained in a superconducting cavity is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We believe that cooling conditions have an additional impact, as they appear to influence the amount of trapped flux and hence the residual resistance. We constructed a test stand using a niobium rod shorted out by a titanium rod to mimic a cavity in its helium tank to study flux trapping. Here we can precisely control the temperature and measure the dynamics of flux trapping at the superconducting phase transition. We learned that magnetic flux can be generated when a temperature gradient exists along the rod and when the niobium transitions into the superconducting state it subsequently remains trapped. Furthermore, it was shown that the cooling rate during isothermal cooldown through the transition temperature can influence the amount of externally applied flux which remains trapped. The acquired knowledge may be used to modify the cooldown procedure of SRF cavities leading to a reduced level of trapped flux and hence operation closer to the BCS limit.
	Slides TUIOA01 [1.276 MB]

TUIOA02	High Q0 Research: The Dynamics of Flux Trapping in Superconducting Niobium	cavity, experiment, simulation, shielding	374
	J.M. Vogt HZB, Berlin, Germany J. Knobloch, O. Kugeler BESSY GmbH, Berlin, Germany
	The quality factor Q0 that can be obtained in a superconducting cavity is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We believe that cooling conditions have an additional impact, as they appear to influence the amount of trapped flux and hence the residual resistance. We have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and measure the dynamics of flux trapping at the superconducting phase transition. We learned that magnetic flux can be generated when a temperature gradient exists along the rod as the niobium transitions to the superconducting state, which subsequently remains trapped. It was also shown that the cooling rate can influence the amount of externally applied flux which is trapped. Furthermore, we also were able to demonstrate that flux lines become mobile if the superconductor is warmed close to below Tc. The acquired knowledge may be used to modify the cooldown procedure of SRF cavities leading to a reduced level of trapped flux and hence operation closer to the BCS limit.
	Slides TUIOA02 [5.774 MB]

TUIOA05	New Insights Into Quench Caused by Surface Pits in SRF Cavities	cavity, laser, SRF, feedback	378
	Y. Xie, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work supported by NSF Career award PHY-0841213 and the Alfred P. Sloan Foundation. Surface defects such as pits have been identified as some of the main sources of limitations of srf cavity performance. A single cell cavity with 30 artificial pits in the high magnetic field region was made to gain new insight in how pits limit the cavity performance. The test of the pit cavity showed clear evidence that the edges of two of the largest radius pits transitioned into the normal conducting state at field just below the quench field of the cavity, and that the quench was indeed induced by these two pits. The pit geometrical information measured by laser confocal microscopy combined with a numerical finite element ring-type defect model will be compared with temperature mapping results. Insights about quench and non-linear rf resistances will be presented. Y. Xie, PhD thesis, Cornell University, 2013
	Slides TUIOA05 [3.101 MB]

TUIOB01	R&D Progress in SRF Surface Preparation With Centrifugal Barrel Polishing (CBP) for both Nb and Cu	cavity, SRF, synchrotron, experiment	398
	A.D. Palczewski JLAB, Newport News, Virginia, USA B. Bullock Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA C.A. Cooper Fermilab, Batavia, USA S.C. Joshi RRCAT, Indore (M.P.), India A. Navitski DESY, Hamburg, Germany A.A. Rossi INFN/LNL, Legnaro (PD), Italy
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Centrifugal Barrel polishing (CBP) is becoming a common R&D tool for SRF cavity preparation around the word. During the CBP process a cylindrically symmetric SRF cavity is filled with relatively cheap and environmentally friendly abrasive and sealed. The cavity is then spun around the cylindrical axis at high speeds uniformly conditioning the inner surface. This uniformity is especially relevant for SRF application because many times a single manufacturing defects limits cavity’s performance well below it’s theoretical limit. In addition CBP has created surfaces with roughness’s on the order of 10’s of nm which create a unique surface for wet chemistry or thin film deposition. CBP is now being utilized at Jefferson Laboratory, Fermi Laboratory and Cornell University in the US, Ko Enerugi Kasokuki Kenkyu Kiku in Japan, Deutsches Elektronen-Synchrotron in Germany, Laboratori Nazionali di Legnaro in Italy, and Raja Ramanna Centre for Advanced Technology in India. In this talk we will present current CBP research from each lab including polishing recipes, equipment, post CBP chemistry/heat treatment, and subsequent cryogenic cavity tests on niobium as well as copper cavities.
	Slides TUIOB01 [2.204 MB]

TUIOC02	Bipolar EP: Electropolishing without Fluorine in a Water Based Electrolyte	cavity, SRF, experiment, controls	404
	A.M. Rowe, A. Grassellino Fermilab, Batavia, USA T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, USA
	Funding: Operated by Fermi Research Alliance, LLC under contract No. De-AC02-07CH11359 with the United States Department of Energy For more than thirty years, preparing superconducting RF cavities for high performance has required the use of dangerous and ecologically damaging chemicals. Reducing the personnel and environmental risks associated with using these chemicals is a priority at Fermilab. Therefore, Fermilab pursued a project to adapt a non-hazardous and relatively benign bipolar electropolishing technique to SRF cavities that Faraday Technology, Inc. developed. Faraday initially developed this electropolishing technique to polish metal alloys used in automotive and semiconductor components as well as medical devices and implants. By modifying the cathodic/anodic interaction via a pulse forward/pulse reverse technique, Fermilab and Faraday Technology demonstrate the capability to polish 1.3 GHz single-cell cavities utilizing an aqueous 10% sulfuric acid electrolyte. We present the development of bipolar EP for single-cell 1.3 GHz cavities and show the results from vertical tests achieving gradients greater than 40 MV/m.
	Slides TUIOC02 [1.251 MB]

TUIOC03	Fluorine Free Ionic Liquid Electropolishing of Niobium Cavities	cavity, cathode, experiment, superconductivity	410
	V.B. Pastushenko, O.V. Malkova, V. Palmieri, A.A. Rossi, F. Stivanello, G. Yu INFN/LNL, Legnaro (PD), Italy G. Yu CIAE, Beijing, People's Republic of China
	Ionic liquids are an emerging breakthrough in green chemistry since the years 2000. In 2006, INFN-LNL was the first to apply a mixture of Choline Chloride and Urea to Niobium electropolishing. It was found that mirror like surfaces could be obtained at temperature higher than 120°C, with high throwing power. Subsequently the process was successfully applied to the electropolishing of a 6 GHz monocell cavity with the addition of sulphamic acid. In this work, we will report an intense investigation of the possible variants of the original recipe. We studied the influence on Niobium surface roughness of several parameters such as: other sulphamic, ammonium and carboxylic containing additives different than sulfamic acid, the possible substitution of Urea with ethylene glycol and malic acid, the current regime; the electrolyte temperature and the cathode shape, rotating horizontal electropolishing versus vertical electropolishing. Due to the cavity hollow cylindrical shape, the electrolyte temperature appeared to be the most crucial parameters among those above mentioned for a uniform dissolution of niobium.
	Slides TUIOC03 [14.464 MB]

TUIOC04	Analysis of Post-Wet-Chemistry Heat Treatment Effects on Nb SRF Surface Resistance	cavity, SRF, superconductivity, site	414
	P. Dhakal, G. Ciovati, P. Kneisel, G.R. Myneni JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Most of the current R&D in SRF is focused on ways to reduce the construction and operating cost of SRF-based accelerators as well as on the development of new or improved cavity processing techniques. The increase in quality factors is the result of the reduction of the surface resistance of the materials. A recent test [] on a 1.5 GHz single cell cavity made from ingot niobium of medium purity and heat treated at 1400 C in a ultra-high vacuum induction furnace resulted in a residual resistance of ~ 1nanoohm and a quality factor increasing with field up to ~ 5×10¹⁰ at a peak magnetic field of 90 mT. In this contribution, we present some results on the investigation of the origin of the extended Q0-increase, obtained by multiple HF rinses, oxypolishing and heat treatment of “all Nb” cavities. [] P. Dhakal et al., Phys. Rev. ST Accel. Beams 16, 042001 (2013).
	Slides TUIOC04 [4.838 MB]

TUIOC05	Purification of 6 GHz Cavities by Induction Heating	cavity, induction, vacuum, SRF	419
	A.A. Rossi, A. Battistello, M. Checchin, V. Palmieri, S. Stark, F. Stivanello, R.K. Thakur, G. Yu INFN/LNL, Legnaro (PD), Italy
	We have developed an innovative technique for purification of bulk-Nb 6GHz RF cavities under ultra-high vacuum (UHV) system. The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect statistics of surface treatments and RF test. Cavities are RF tested before and after high temperature treatment under UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher than 2000°C and close to the melting point of Nb for less than a minute while few seconds at maximum temperature. Before RF test and UHV annealing, the surface treatment processes like tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high pressure rinsing (HPR) have been employed. This kind of Nb 6 GHz cavity purification allow to reduce hydrogen, oxygen and other elemental impurities content, which effects on cavity Q-factor degradation, by a rapid annealing over 2000°C and a subsequent rapid reduction at room temperature.
	Slides TUIOC05 [42.171 MB]

TUIOC06	Study on Optimum Electron Beam Welding Condition for Superconducting Accelerating Cavities	cavity, electron, experiment, SRF	424
	T. Kubo, Y. Ajima, H. Inoue, T. Saeki, K. Umemori, Y. Watanabe, S. Yamaguchi, M. Yamanaka KEK, Ibaraki, Japan T. Nagata ULVAC, Inc., Tsukuba, Japan
	Optimizations of electron beam welding conditions might solve the quench problems and improve the accelerating field of the superconducting radio-frequency cavity. As a first step toward optimum conditions, basic properties of weld beads are studied by using niobium test pieces. Effects of a combination of a beam generator position and a welding direction on geometries of weld bead are shown. Good parameter-regions for electron beam welding, which yield full penetration welds without holes or weld spatters, are surveyed. Microscopic structures, such as pits or bumps due to poor welds, have greater influence on cavity performances, which are also our research objects. We introduce a model of the magnetic field enhancement at pits, where a formula for a magnetic field enhancement factor is given as a function of parameters that express a geometry of pit. Comparisons between calculations and vertical test results are also shown.
	Slides TUIOC06 [15.958 MB]

TUP009	Magnetic Dependence of the Energy Gap: a Good Model to Fit Q Slope of Low Beta Cavities	cavity, superconductivity, experiment, simulation	438
	D. Longuevergne IPN, Orsay, France
	The reasons why the intrinsic quality factor (noted Qo) of a superconducting cavity drops with the accelerating field (noted Eacc) are still not well understood. In an effort to explain this phenomenon, mainly for high beta cavities, many models have been developed in the community but few of them could fit experimental data whatever the material treatment or surface conditioning. In the specific case of low beta cavities made of bulk Niobium (i.e Spiral 2 Quarter Wave Resonator), a model based on a magnetic field dependence of the energy gap has been developed to fit experimental data. The evolutions of the model input parameters depending on the cavity treatment or test conditions are consistent with the changes described in the literature. The model will be described and specific examples will be given.

TUP010	Simulation of Non-linear RF Losses Derived from Characteristic Nb Topography	cavity, simulation, SRF, interface	441
	C. Xu, M.J. Kelley JLAB, Newport News, Virginia, USA M.J. Kelley, C. Xu The College of William and Mary, Williamsburg, USA C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A simplified model has been developed to simulate non-linear rf losses on Nb surfaces due exclusively to topographical enhancement of surface magnetic fields. If local sharp edges are small enough, where local surface fields exceed Hc, small volumes of material may become normal conducting without thermal runaway leading to quench. These small volumes of normal material yield increases in the effective surface resistance of the Nb. Using topographic data from typical BCP’d and EP’d fine grain niobium, we have simulated field-dependent losses and find that when extrapolated to resulting cavity performance correspond well to characteristic BCP/EP high field Q0 performance differences for fine grain Nb. We will describe the structure of the model, its limitations, and the effects of this type of non-linear loss contribution to SRF cavities.

TUP011	A Parametric Study of BCS RF Surface Impedance with Magnetic Field Using Xiao Code	impedance, SRF, superconductivity, survey	444
	C.E. Reece JLab, Newport News, Virginia, USA B. P. Xiao JLAB, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A recent new analysis of field-dependent BCS RF surface impedance based on moving Cooper pairs has been presented.* Using this analysis coded in Mathematica™, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the “best theoretical” performance available to potential applications with corresponding materials. * Xiao B. P. et al, Physica C: Superconductivity, 490, 2013, pp. 26–31

TUP014	Fast Table Top Niobium Hydride Investigations Using Direct Imaging in a Cryo-Stage	cavity, cryogenics, laser, vacuum	447
	F.L. Barkov, A. Grassellino, A. Romanenko Fermilab, Batavia, USA
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. Performance of niobium SRF cavities can be strongly affected by hydrogen segregation into lossy niobium hydrides as known for "hydrogen Q disease" at higher concentration of dissolved H and may be a reason for the "high field Q slope" at lower concentrations. With the use of optical cryostat and laser confocal microscope we have developed a "table top technique" for direct observation of hydride precipitation, and studied formation, morphology, and time evolution of hydrides after different treatments used for cavities. Our results show that hydrides can form at the niobium surface at 90-180K depending mainly on H concentration and the cooldown rate. A lot of H is absorbed by bulk niobium during mechanical polishing, which leads to the formation of very large (>10 microns) hydrides. Both EP and BCP do not influence H concentration significantly provided that temperature during treatments is kept below 15C. 800C degassing reduces H concentration and precludes large hydride precipitation. 120C baking and mechanical deformation do not change H concentration but affect hydride precipitation through their influence on the number of nucleation centers and H binding defects.

TUP015	Bitter Decoration Studies of Magnetic Flux Penetration Into Cavity Cutouts	SRF, experiment, cavity, radio-frequency	451
	F.L. Barkov, A. Grassellino, A. Romanenko Fermilab, Batavia, USA L.Y. Vinnikov ISSP, Chernogolovka, Russia
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. Magnetic flux penetration may produce additional losses in superconducting radio frequency cavities. All the existing models for flux penetration are based on the formation of Abrikosov vortices. Using high resolution Bitter decoration technique we have investigated magnetic flux distribution patterns in cavity cutouts at the perpendicular magnetic fields of 10-80 mT. At low fields <20 mT the magnetic field penetrates in the form of flux bundles and not Abrikosov vortices, the situation characteristic of type-I superconductors. With the increase of the magnetic field up to 30 mT "bundles" first merge into a connected structure and then break up into individual Abrikosov vortices at ~60 mT and a well-known intermediate mixed state is observed. Such magnetic field driven transition from type I to type II superconductivity has never been observed before in any existing superconductor. For the case of flat samples we have observed a coexistence of both "bundles" and Abrikosov vortices in one experiment. Our results show that high-purity cavity grade niobium is a "border-line" material and behaves as a type-I superconductor at lower fields and type-II at higher fields.

TUP016	Effects of Processing History on Damage Layer Evolution in Large Grain Nb Cavities	cavity, SRF, electron, radio-frequency	455
	D. Kang, T.R. Bieler Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222. Previous cavity tests identified a strong dependence of achievable accelerating gradients on the amount of material removed from the surface. Samples extracted from the iris and the equator of a half cell fabricated by Jefferson Lab using large grain Nb were examined to identify underlying mechanisms. Electron backscattered diffraction (EBSD) was used to measure the crystal orientations on the cross sections of the samples. Results demonstrated the presence of a surface damage layer, which contained higher dislocation content than the bulk due to the deep drawing process. The depth of the damage layer depends on crystal orientations, and damage to the iris is more severe than at the equator. From the EBSD data, the damage depth was estimated to be about 100 microns. The samples were then heat treated at 800°C and 1000°C, and the same areas were examined again for the effects of heat treatment on the healing of the damage layer. While the damage layer accounts for some of the performance gain from chemical surface removal, the depth of the damage layer in polycrystalline cavities remains an open question.

TUP017	Study of Slip and Dislocations in High Purity Single Crystal Nb for Accelerator Cavities	cavity, SRF, radio-frequency, factory	461
	D. Kang, D.C. Baars, T.R. Bieler Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222. SRF Cavities can be formed by deep drawing slices from Nb ingots with large grains. Crystal orientation dependent slip system activities affect the shape change of ingot slices during deep drawing, and form a dislocation substructure that affects subsequent recrystallization and ultimately, cavity performance. Two groups of single crystal tensile specimens with different orientations were extracted from a large grain ingot slice. The first group was deformed monotonically to 40% engineering strain. Analysis revealed that slip was preferred on {112} planes. The second group was heat treated at 800°C for two hours, and then deformed incrementally to 40% engineering strain using an in situ tensile stage. Crystal orientations and surface images were recorded at each increment of deformation. Results indicate that the heat treated group had lower yield strengths, and the details of slip activity differed in the annealed samples. Active slip systems were investigated and compared to the first group. Direct observations of dislocations were performed in selected specimens using electron channeling contrast imaging, to determine how slip affects the dislocation substructure.

TUP022	Study of AC/RF Properties of SRF Ingot Niobium	cavity, SRF, radio-frequency, superconductivity	469
	P. Dhakal, G. Ciovati, G.R. Myneni JLAB, Newport News, Virginia, USA V.M. Genkin, M.I. Tsindlekht The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem, Israel
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In an attempt to correlate the SRF performance of niobium cavities with the superconducting properties, we present the results of the magnetization and ac susceptibility of the niobium used in the superconducting radiofrequency cavity fabrications which were subjected to buffer chemical polishing surface and high temperature heat treatments, typically applied to the SRF cavities fabrications. The analysis of the results show the different surface and bulk ac conductivity for the samples subjected to BCP and HT. Furthermore, the RF surface impedance is measured on the sample using the TE011 microwave cavity for a comparison to the low frequency measurements.

TUP023	Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities	SRF, site, superconducting-RF, superconductivity	472
	G.V. Eremeev, A.D. Palczewski JLAB, Newport News, Virginia, USA
	Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique[]. The data differed from measurements done in 80’s that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields and RF resistances at the breakdown site. [] G. Eremeev et al.,. In Proceedings of the 15th Superconducting RF conference,pp. 746-749, July 2011.

TUP026	Performance of a FNAL Nitrogen Treated Superconducting Niobium Cavity at Cornell	cavity, SRF, linac, superconductivity	475
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A. Grassellino Fermilab, Batavia, USA
	Funding: NSF In many tests of superconducting cavities, the performance of the cavity in the medium field region will be limited by medium field Q slope. For projects such as the proposed Cornell Energy Recovery Linac, high Q operation at medium fields is necessary to meet specifications for efficient CW cavity operation. A single cell cavity was prepared by Fermilab by electropolishing it and baking it at 1000°C with 1x10^-2 Torr of Nitrogen, and subsequently tested at Cornell. The cavity displayed an increase in Q at medium fields between 5 and 20 MV/m at 2.0 K, opposite of the usual medium field Q slope. The material properties of this cavity were studied and correlated with performance. This analysis helps to better understand how to overcome medium field Q slope and improve cavity performance in future CW SRF machines such as the Cornell ERL.

TUP027	High Q0 Studies at Cornell	cavity, SRF, factory, linac	478
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF The construction and preparation of superconducting RF cavities with very high quality factors is very advantageous for future particle accelerators operating in CW mode. Until recently, the highest quality factors measured in SRF cavities were on the order of 10¹¹. A Cornell ERL single-center-cell cavity was prepared with BCP and a five day heat treatment at 1000°C. Following this treatment, the cavity was tested and achieved a record high intrinsic quality factor of 2.9·10¹¹ at 1.4 K, corresponding to a very small residual resistance of (0.35±0.10) nOhm. This cavity was then given a series of BCP’s of 5, 75, and 200 μm and retested. Material properties were extracted from the data hinting at a very low mean free path of the niobium. In this paper we discuss the unusual material properties of the surface layer of the cavity and their implication for the RF performance of the cavity.

TUP029	Heat Treatment of SRF Cavities in a Low-Pressure Atmosphere	cavity, vacuum, SRF, resonance	487
	D. Gonnella, F. Furuta, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Recent results from FNAL on baking superconducting RF cavities at high temperatures in a low-pressure atmosphere of a few mTorr indicate that such treatments can increase the medium field quality factor. In this paper we report on studies from Cornell, giving new insight into the mechanism behind this effect.

TUP033	Magnetic Property Improvement of Niobium Doped with Rare Earth Elements	cavity, experiment, SRF, electron	490
	F.S. He, F. He, F. Jiao, X.Y. Lu, K. Zhao PKU, Beijing, People's Republic of China L. Chen NNIEC, Shizuishan City, Ningxia, People's Republic of China T.C. Jiang IMP, Lanzhou, People's Republic of China Y. You, H.Y. Zhao Ningxia Orient Tantalum Industry Co., Ltd., Dawukou District, Shizuishan city, People's Republic of China
	A new idea of modifying the raw niobium was proposed by PKU in 2010, by introducing rare earth elements of Sc and Y into Nb ingot during smelting process. Test results on small samples were very promising: the Tc was same as Nb, while the Hc1 and Hc2 were increased by 500-700 Oe and up to 4000 Oe, respectively. Recently one Nb ingot doped with Sc was successfully smelted under the collaboration of PKU and OSTEC at Ningxia, and two TESLA-type half cells were fabricated out of the new material by deep drawing. The Hc1 measured from the drop-off of the blanks were consistently high. The RRR was 127, while the mechanical properties met the ILC requirement. One single cell cavity is being fabricated, and vertical test is planned to study the SRF properties of the new material. There is a good chance that the quenching could be pushed to a higher gradient. Another innovative idea of doping only the surface layer of bulk Nb by ion implantation in the pelletron at PKU is also being investigated, in order to improve the SRF performance of the surface layer while maintaining the high thermal conductivity of bulk Nb. Some initial testing results of the new method will be reported as well. TTC2012 at JLab: https://www.jlab.org/indico/getFile.py/access?contribId=78&sessionId=8&resId=0&materialId=slides&confId=24

TUP037	Dynamic Hardening Rule; a Generalization of the Classical Hardening Rule for Crystal Plasticity	experiment, simulation, SRF, controls	499
	A. Mapar, F. Pourboghrat MSU, East Lansing, USA T.R. Bieler Michigan State University, East Lansing, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222. The mechanical properties of a niobium (Nb) specimen can change with the orientation of the sheet. This anisotropy causes inhomogeneity in manufactured SRF cavities. Large grain Nb sheets are more anisotropic and less expensive than fine grain sheets. Designing a manufacturing process for large grain Nb sheets, however, is extremely complex, and requires using advance modeling techniques. A model capable of accurately predicting the deformation behavior of Nb can help improve the performance and reduce costs of a SRF cavity. Optimal design of the manufacturing of cavities with tube hydroforming process is possible with such a model. Crystal plasticity modeling of FCC materials has been very successful; however, there is still no model that can accurately predict the deformation behavior of BCC materials like the large grain Nb sheet. In this study, authors have proposed a dynamic hardening rule for crystal plasticity that significantly improves predictions of the model for large grain Nb. This model is the generalization of the classical hardening rule, and gives better control over the hardening rate. It also increases the stability of the model.

TUP043	Nanostructural TEM/STEM Studies of Hot and Cold Spots in SRF Cavities	cavity, electron, SRF, vacuum	504
	Y. Trenikhina, J. Zasadzinski IIT, Chicago, USA A. Romanenko Fermilab, Batavia, USA
	Direct TEM/STEM imaging and spectroscopic chemical characterization by EELS/EDS of the surface of the SRF cavity cutouts before and after the treatments (e.g. in situ mild vacuum bake and rinsing with hydrofluoric acid) down to subnanometer scale is implemented to correspond the changes in niobium surface to the SRF performance of the cavities. We also report current results of the direct search, using cryogenic TEM stage, for suggested phase transformations in the niobium-hydrogen system* on “hot” and “cold” spot cavity cutouts, which may help clarifying the mechanism of the high field Q slope and its empirical cure. *A. Romanenko, F. Barkov, L. D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26 (2013) 035003.

TUP047	Niobium Cavity Electropolishing Modelling and Optimisation	cathode, SRF, simulation, cavity	518
	L.M.A. Ferreira, S. Calatroni, S. Forel CERN, Geneva, Switzerland J.A. Shirra Loughborough University, Leicestershre, United Kingdom
	It’s widely accepted that electropolishing is the most suitable surface finishing process to achieve high performance bulk Nb accelerating cavities. At CERN, as part of the R&D studies for the 704 MHz high-beta SPL cavities, a new vertical electropolishing facility has been assembled and a study is on-going for the modelling of electropolishing on cavities with COMSOL software. In a first phase, the electrochemical parameters were taken into account for a fixed process temperature and flow rate, and are presented in this poster as well as the results obtained on a real SPL single cell cavity. The procedure to acquire the data used as input for the simulation is presented. The modelling procedure adopted to optimise the cathode geometry, aimed at a uniform current density distribution in the cavity cell for the minimum working potential and total current is explained. Some preliminary results on fluid dynamics and Joule effect are also briefly described.

TUP052	Study on Vertical Electro-Polishing by Cathode With Variable-Geometry Wings	cavity, experiment, cathode, scattering	530
	Y.I. Ida, K.N. Nii MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi, Y.B. Iwabuchi MGI, Chiba, Japan
	We have been studying on Vertical Electro-Polishing (VEP) of Nb superconducting accelerator cavity for about one year with a view to the mass-production and cost-reduction of Electro-Polishing (EP) process. Marui Galvanizing Co. Ltd. has been in the EP business of various metals for long time and we have matured experience on EP processes. With being based on the experience, we thought that uniform electric-current on the surface of cavity and effective flow of electrolyte in the cavity are important factors. Moreover, we thought the most important effect is given if the cathode and the cavity surface (anode) are kept in a constant distance. Following these considerations, we invented VEP process by a cathode with variable-geometry wings. Using this cathode, we performed several experiments of VEP Nb single-cell cavities as well as fluid circulation test by plastic 9-cell mock-up. In this article, we will report this unique VEP process, which might be applicable to the mass-production process of International Linear Collider (ILC).

TUP054	Electropolishing of Niobium SRF Cavities in Low Viscosity Aqueous Electrolytes Without Hydrofluoric Acid	cavity, SRF, experiment, controls	540
	E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder Faraday Technology, Inc., Clayton, USA A.M. Rowe Fermilab, Batavia, USA
	Funding: U.S. DOE Purchase order No. 594128 Electropolishing of niobium materials and cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acid. The use of these dangerous and ecologically damaging chemicals requires careful attention to safety protocol to avoid harmful worker exposure and environmental damage. In this poster we present an approach based on bipolar voltage fields enabling the use of low viscosity water based electrolytes without hydrofluoric acid for electropolishing of niobium materials. The subtleties of the bipolar electropolishing process vis-a-vis conventional electropolishing will be presented.

TUP055	Electropolishing of the ANL Deflecting Cavity for the APS Upgrade	cavity, SRF, background, coupling	544
	Y. Yang, J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu ANL, Argonne, USA A.C. Crawford Fermilab, Batavia, USA P. Dhakal, J.D. Mammosser, H. Wang JLAB, Newport News, Virginia, USA Y. Yang TUB, Beijing, People's Republic of China
	Studies on the application of electropolishing (EP) of the ANL superconducting deflecting cavity have shown promising results. This cavity geometry is a squashed single-cell cavity with Y-end group waveguide as well as on-cell LOM damper. The cavity works at TM110-like deflecting mode, in which the iris between the cavity cell and the Y-end group is the highest magnetic field region. Before EP, the cavity had been chemically etched (BCP) several times. Forty-um EP processing was performed on one Mark II prototype deflecting cavity at Fermilab. No mild baking was performed before the cavity vertical test. The test showed that the low-field Q had improved from 2·10⁹ to 3·10⁹ and the high-field Q-slope had been successfully removed. The quench limit was slightly improved from 10⁶ mT to 113 mT. Fast T-mapping had detected a significant decrease of local temperature rise in the cavity iris. Optical inspection before EP found a lot of grooves around the iris, which might be related to the gas bubbles generated during BCP. This suggests that horizontal EP is a promising processing technique to remove the high-field Q-slope and improve the deflecting cavity performance.

TUP057	Plasma Processing R&D for the SNS Superconducting Linac RF Cavities	plasma, cavity, linac, cryomodule	551
	M. Doleans, W. Blokland, M.T. Crofford, D.L. Douglas, M.P. Howell, S.-H. Kim, P.V. Tyagi ORNL, Oak Ridge, Tennessee, USA R. Afanador, J.A. Ball, B. DeGraff, B.S. Hannah, S.W. Lee, C.J. McMahan, J. Saunders ORNL RAD, Oak Ridge, Tennessee, USA
	Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE The Spallation Neutron Source routinely operates with a proton beam power of 1 MW on its production target. A plan to reach the design 1.4 MW within a few years is in place* and relies on increasing the ion beam current, pulse length and beam energy in the linac. The increase in beam energy from the present 930 MeV to 1 GeV will require an increase of approximately 15% in the accelerating gradient of the superconducting linac high-beta cryomodules. In-situ plasma processing was identified as a promising technique** to reduce electron activity in the SNS superconducting cavities and increase their accelerating gradient. R&D on plasma processing aims at deploying the new in-situ technique in the linac tunnel by 2016. Overall plan and current status of the plasma processing R&D will be presented. * NScD Five year plan 2012-2016, SNS-NSCD-EXE-PN-0001, R00, ORNL ** S-H Kim et al., “R&D Status for In-Situ Plasma Surface Cleaning of SRF Cavities at Spallation Neutron Source”, PAC 2011 Proceedings

TUP058	Recent Findings on Nitrogen Treated Niobium	cavity, SRF, vacuum, solenoid	558
	R.G. Eichhorn, A. Ganshin, A. Holmes, J.J. Kaufman, S.R. Markham, S. Posen, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Recent findings on Nitrogen treated Niobiums Based on recent findings at Fermilab, Cornell investigated the role of Nitrogen being present during the cavity hydrogen degassing process. We treated several samples at different temperatures being exposed to nitrogen between 10 minutes and 3 hours at pressures around 15 mbar as well as single cell cavities. This contribution will summarize our findings from surface analysis, Tc measurements and cavity Qs, addressing the question, if such a process can form Niobium-Nitride.

TUP060	Acid Free Extended Mechanical Polishing R&D	cavity, SRF, electron, radio-frequency	564
	C.A. Cooper, A.C. Crawford, C.M. Ginsburg, A. Grassellino, R.D. Kephart, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov Fermilab, Batavia, USA
	We report the progress in the development of a centrifugal barrel polishing recipe which can lead to standard cavity performance without the need of any chemical treatments. Q ~ 10¹⁰ at 20 MV/m and gradients above 35 MV/m have already been demonstrated for cavities whose preparation sequence was CBP, degassing and no subsequent chemical treatments. Results of studies on the effect of different CBP media on RF performance will be reported, including full body T-map showing the distribution of RF losses.

TUP062	Application of In-Vacuum Infrared Pyrometry During Fabrication of European XFEL Niobium Cavities	cavity, vacuum, operation, electron	570
	L. Monaco, P. Michelato, D. Sertore INFN/LASA, Segrate (MI), Italy V. Battista, G. Corniani, M. Festa Ettore Zanon S.p.A., Schio, Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	A technique to measure the temperature of Niobium components in vacuum during Electron Beam Welding (EBW) operation is presented and results obtained on the large scale cavity production for the European XFEL are discussed. During the EBW process, the knowledge of the components temperature during the welding operation could help both for the better choice of the welding parameters and for the optimization of the production cycle. In collaboration with the Italian firm Ettore Zanon (EZ), we developed a system able to measure the temperature of Nb components in vacuum during EBW operation using a IR pyrometer placed outside the vacuum chamber through an appropriate vacuum viewport. In the paper the experience of this device during the production of Nb components for the XFEL 1.3 GHz cavity production is discussed.

TUP063	Quench Studies and Preheating Analysis of Seamless Hydroformed Cavities Processed at Jefferson Laboratories	cavity, SRF, electron, site	575
	A.D. Palczewski, G.V. Eremeev, R.L. Geng JLAB, Newport News, Virginia, USA I. Jelezov RAS/INR, Moscow, Russia W. Singer, X. Singer DESY, Hamburg, Germany
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. One of the alternative manufacturing technologies for SRF cavities is hydroforming from seamless tubes. Although this technology has produced cavities with gradient and Q-values comparable to standard EBW/EP cavities, a few questions remain. One of these questions is whether the quench mechanism in hydroformed cavities is the same as in standard electron beam welded cavities. Towards this effort Jefferson Lab performed quench studies on 4 different seamless hydroformed cavities. These cavities include DESY’s – Z163 and Z164 nine-cell cavities, and Black Laboratories nine-cell and two-cell TESLA shaped cavities, hydroformed at DESY. Initial results from the cavities and quench localization were published in SRF2011. In this report we will present post JLAB surface retreatment quench studies for each cavity. The data will include OST and T-mapping quench localization as well as quench location preheating analysis comparing them to the observations in standard electron beam welded cavities. W. Singer, A. Ermakov, G. Kreps, A. Matheisen, X. Singer, K. Twarowski, I. Zhelezov, P. Kneisel, R. Crooks, Proceedings of SRF2011, TUPO026 2011.

TUP064	Exploration of Material Removal Rate of SRF Elliptical Cavities as a Function of Media Type and Cavity Shape on Niobium and Copper Using Centrifugal Barrel Polishing (CBP)	cavity, SRF, superconductivity, status	579
	A.D. Palczewski, G. Ciovati, R.L. Geng, Y.M. Li JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Centrifugal barrel polishing (CBP) for SRF application is becoming more wide spread as the technique for cavity surface preparation. CBP is now being used in some form at SRF laboratories around the world. Before the process can become as mature as wet chemistry like eletro-polishing (EP) and buffered chemical polishing (BCP) there are many questions which remain unanswered. One of these topics includes the uniformity of removal as a function of cavity shape and material type. In this presentation we show CBP removal rates for various media types on 1.3 GHz TESLA and 1.5 GHz CEBAF large grain niobium cavities, 1.3 GHz TESLA fine grain niobium cavity, and 1.3GHz low surface field copper cavity. The data will also include calculated RF frequency shift modeling non-uniform removal as a function of cavity position and comparing them with CBP results.

TUP065	Chemical Structure of Niobium Samples Vacuum Treated in Nitrogen in Parallel With Very High Q0 Cavities	cavity, SRF, lattice, accelerating-gradient	583
	Y. Trenikhina IIT, Chicago, USA A. Grassellino, A. Romanenko Fermilab, Batavia, USA
	XPS in combination with subsequent material removal via Ar sputtering as well as XRD are used for the surface analysis and bulk phase characterization of nitrogen treated samples processed parallel with SRF cavities. We investigated the surface chemistry of the samples treated with nitrogen in order to understand this treatment effect on SRF cavity performance for several baking temperatures and durations in order to find cost efficient post-furnace chemistry free procedures to enable high Q-values.

TUP066	Plasma Processing of Large Surfaces with Application to SRF Cavity Modification	plasma, cavity, SRF, experiment	586
	J. Upadhyay, S. Popović, L. Vušković ODU, Norfolk, Virginia, USA D.S. Im Old Dominion University, Norfolk, Virginia, USA H.L. Phillips, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA
	Funding: Supported by DOE under grant no. DE-SC0007879. JU acknowledges support by JSA/DOE via DE-AC05-06OR23177 Plasma based surface modifications of SRF cavities present promising alternatives to the wet etching technology currently applied. To understand and characterize the plasma properties and chemical kinetics of plasma etching processes inside a single cell cavity, we have built a specially-designed cylindrical cavity with 8 observation ports. These ports can be used for holding niobium samples and diagnostic purposes simultaneously. Two frequencies (13.56 MHz and 2.45 GHz) of power source are used for different pressure, power and gas compositions. The plasma parameters were evaluated by a Langmuir probe and by an optical emission spectroscopy technique based on the relative intensity of two Ar 5p-4s lines at 419.8 and 420.07 nm. Argon 5p-4s transition is chosen to determine electron temperature in order to optimize parameters for plasma processing. Chemical kinetics of the process was observed using real-time mass spectroscopy. The effect of these parameters on niobium surface would be measured, presented at this conference, and used as guidelines for optimal design of SRF etching process.

TUP067	Hydrogen Saturation and the Thermal Conductivity of Superconducting Niobium	cavity, superconductivity, vacuum, lattice	589
	S.K. Chandrasekaran MSU, East Lansing, USA T.R. Bieler Michigan State University, East Lansing, USA C. Compton FRIB, East Lansing, USA N.T. Wright (MSU), East Lansing, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222 The thermal conductivity k of Nb at less than 3 K is dominated by phonon transport. In Nb with sufficiently few lattice imperfections, a maximum in k occurs at 1.8 K, called the phonon peak (PP). A large PP is desired to reduce potential local hot spots and contributes to an increased Q factor. The magnitude of the PP is sensitive to SRF cavity manufacturing processes. The effect of interstitial hydrogen on the magnitude of the PP is examined by subjecting two bicrystal Nb specimens to 300 C for 1 h in a 75% H2, 25% N2 atmosphere at 0.5 atm. Prior to hydrogen infusion, specimen 1 was heated to 800 C for 2 h, while specimen 2 was heated to 1100 C for 4 h. Both specimens displayed a 25% reduction in the PP due to the additional hydrogen, independent of their crystal orientations and heat treatment histories. An 800 C vacuum heating for 2 h was found to be sufficient to recover the PP in specimen 1, while an 1100 C heating for 4 h was required to recover the PP in one of the grains of specimen 2. The results suggest that hydrogen trapped in the Nb lattice will degas when the Nb is heated to at least the temperature to which it was heated at prior to the hydrogen infusion step.

TUP068	Laser Polishing of Niobium for SRF Applications	laser, experiment, SRF, simulation	593
	L. Zhao, M.J. Kelley The College of William and Mary, Williamsburg, USA M.J. Kelley, J.M. Klopf, C.E. Reece JLAB, Newport News, Virginia, USA L. Zhao JLab, Newport News, Virginia, USA
	Smooth interior surfaces are desired for niobium SRF cavities, now obtained by buffered chemical polish (BCP) and/or electropolish (EP). Laser polishing is a potential alternative, having advantages of speed, freedom from chemistry and in-process inspection. Here we show that laser polishing can produce smooth topography with Power Spectral Density (PSD) measurements similar to that obtained by EP. We studied the influence of the laser power density and laser beam raster rate on the surface topography. These two factors need to be combined carefully to smooth the surface without damaging it. Computational modeling was used to simulate the surface temperature and explain the mechanism of laser polishing.
	Poster TUP068 [1.011 MB]

TUP070	Characterization of Superconducting Samples With SIC System for Thin Film Developments: Status and Recent Results.	cavity, ECR, SRF, network	599
	G.V. Eremeev, H.L. Phillips, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA C.E. Reece JLab, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Within any thin film development program directed towards SRF accelerating structures, there is a need for an RF characterization device that can provide information about RF properties of small samples. The current installation of the RF characterization device at Jefferson Lab is Surface Impedance Characterization (SIC) system. The data acquisition environment for the system has recently been improved to allow for automated quicker measurement, and the system has been routinely used for characterization of bulk Nb, films of Nb on Cu, MgB2, NbTiN, Nb3Sn films, etc. We present some of the recent results that illustrate present capabilities and limitations of the system.

TUP071	Development of Nb3Sn Cavity Vapor Diffusion Deposition System	cavity, vacuum, impedance, controls	603
	G.V. Eremeev, W.A. Clemens, K. Macha, H. Park, R.S. Williams JLAB, Newport News, Virginia, USA H. Park ODU, Norfolk, Virginia, USA
	Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Alternative BCS superconductors with the superconducting critical temperature higher than that of niobium theoretically surpass the limitations of niobium. The feasibility of technology has been demonstrated at 1.5 GHz with Nb3Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb3Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb3Sn vapor diffusion deposition system within an R&D development program towards compact light sources. Here we present the current progress of the system development.

TUP072	Quality Factor Measurements of the Ultramet 3 GHz Cavity Constructed Using Chemical Vapour Deposition	cavity, SRF, radio-frequency, operation	607
	D.L. Hall, D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V.M. Arrieta, S.R. McNeal Ultramet, California, USA
	Funding: US Department of Energy Phase 1 Small Business Innovation Research award to Ultramet A seamless 3 GHz bulk niobium cavity constructed by Ultramet using rapid chemical vapor deposition (CVD) techniques has been tested on the vertical SRF test stand at Cornell. The cavity received a 25 um buffered chemical polish (BCP) and 700 C heat treatment for 4 days. First test results gave an intrinsic quality factor of Q0 = (1.55 ± 0.12) x 10⁷ and (2.00 ± 0.15) x 10⁷ at 4.2 K and 1.5 K, respectively. A second BCP removed 100 um of material, after which test results improved to Q0 = (7.59 ± 1.52) x 10⁷ and (4.16 ± 0.31) x 10⁸ at 4.2 K and 1.5 K. During the ﬁrst test poor coupling to the input ampliﬁer impeded tests at accelerating ﬁelds >0.2 MV/m, while during the second test the cavity quenched at 1.3 MV/m when operating at 1.5 K. An optical inspection of the cavity after the second test revealed the presence of at least 4 pits on the upper hemisphere suggesting an area of higher than average surface resistance that may have contributed to the low ﬁeld quench via thermal runaway. The potential of CVD as a construction method for SRF cavities is discussed.

TUP073	Niobium Coatings for the HIE-ISOLDE QWR Superconducting Accelerating Cavities	cavity, vacuum, cathode, SRF	611
	N.M. Jecklin, S. Calatroni, L.M.A. Ferreira, I. Mondino, A. Sublet, M. Therasse, W. Venturini Delsolaro CERN, Geneva, Switzerland B. Delaup EPFL, Lausanne, Switzerland
	The HIE-ISOLDE project is the upgrade of the existing ISOLDE facility at CERN, which is dedicated to the production of a large variety of radioactive ion beams for nuclear physics experiments. A new linac made of 20 β=10.3% and 12 β=6.3% QWR superconducting accelerating cavities at 101 MHz will be built, and in a first phase two cryomodules of 5 high-beta cavities each are scheduled to accelerate first beams in 2015. The cavities are made of a copper substrate, with a sputter-coated superconductive niobium layer, operated at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses (Q0=4.5e8) In this paper we will discuss the baseline surface treatment and coating procedure which allows obtaining the required performance, as well as the steps undertaken in order to prepare series production of the required number of cavities guaranteeing their quality and functionality.

TUP074	Development of an Optimized Quadrupole Resonator at HZB	quadrupole, cavity, resonance, focusing	614
	R. Kleindienst, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Funding: EuCARD II Current superconducting cavities are generally made of solid niobium. A possibility to reduce cost as well as increase accelerating fields and, essential for CW applications, the quality factor is to use thin-film coated cavities. Measuring and understanding the RF-properties of superconducting thin films, specifically the surface resistance at the operating field and frequency, is needed to drive forward this development. Presently, only few facilities exist capable of measuring the surface resistance of thin films samples with a resolution in the nano-ohm range at L-Band. We describe here a dedicated test stand consisting of a quadrupole resonator that was constructed at the Helmholtz Zentrum Berlin. Starting with 400-MHz quadrupole resonator developed at CERN, the design was adapted and optimized for resolution and reduced peak electric field to 433 MHz (making available the higher harmonic mode at 1,3GHz) using simulation data obtained with CST Microwave Studio as well as ANSYS. The relevant figures of merit have been improved, giving the possibility to perform measurements with high resolution at high field levels.

TUP075	Design and Commissioning Status of New Cylindrical HiPIMS Nb Coating System for SRF Cavities	cavity, ion, cathode, SRF	617
	H.L. Phillips, K. Macha, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA
	Funding: † Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. For the past 19 years Jefferson Lab has sustained a program studying niobium films deposited on small samples in order to develop an understanding of the correlation between deposition parameters, film micro-structure, and RF performance. A new cavity deposition system employing a cylindrical cathode using the HiPIMS technique has been developed to apply this work to cylindrical cavities. The status of this system will be presented.

TUP076	Preliminary Results of Nb Thin Film Coating for HIE-ISOLDE SRF Cavities Obtained by Magnetron Sputtering	cavity, plasma, cathode, monitoring	620
	A. Sublet, I. Aviles Santillana, S. Calatroni, A. D'Elia, N.M. Jecklin, I. Mondino, S. Prunet, M. Therasse, W. Venturini Delsolaro, P. Zhang CERN, Geneva, Switzerland
	Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI. In the context of the HIE-ISOLDE upgrade at CERN, several new facilities for the niobium sputter coating of QWR-type superconducting RF accelerating cavities have been developed, built, and successfully operated. In order to further optimize the production process of these cavities the magnetron sputtering technique has been further investigated and continued as an alternative to the already successfully operational DC bias diode sputtering method. The purpose of this poster is to present the results obtained with this technique. The Nb thickness profile along the cavity and its correlation with the electro-magnetic field distribution inside the cavity are discussed. Film structure, morphology and Residual Resistivity Ratio (RRR) will be considered as well and compared with films obtained by DC bias diode sputtering. Finally these results will be compared with RF characterization and measurement of a production-like magnetron-coated cavity.

TUP077	Thin Film Coating Optimization for HIE-ISOLDE SRF Cavities: Coating Parameters Study and Film Characterization	cavity, cathode, hardware, SRF	623
	A. Sublet, I. Aviles Santillana, S. Calatroni, P. Costa Pinto, N.M. Jecklin, S. Prunet, A. Sapountzis, W. Venturini Delsolaro, W. Vollenberg CERN, Geneva, Switzerland
	Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI. The HIE-ISOLDE project at CERN requires the production of 32 cavities in order to increase the energy of the beam. The Quarter Wave Resonators (QWRs) cavities of complex cylindrical geometry (0.3m diameter and 0.8m height) are made of copper and are coated with a thin superconducting layer of niobium. In the present phase of the project the aim is to obtain a niobium film, using the DC bias diode sputtering technique, providing adequate high quality factor of the cavities and to ensure reproducibility for the future series production. After an overview of the explored coating parameters (hardware and process), the resulting film characteristics, thickness profile along the cavity, structure and morphology (SEM measurements) and Residual Resistivity Ratio (RRR) of the Nb film will be shown. The effect of the sputtering gas process pressure and configuration of the coating setup will be highlighted.

TUP078	Nb Coating Developments with HIPIMS for SRF Applications	cavity, target, plasma, cathode	627
	G. Terenziani, I. Aviles Santillana, S. Calatroni, T. Junginger CERN, Geneva, Switzerland A.P. Ehiasarian SHU, Sheffield, United Kingdom
	In the last few years the interest of the thin film science and technology community on High Impulse Power Magnetron Sputtering (HIPIMS) coatings has steadily increased. HIPIMS literature shows that better thin film morphology, denser and smoother films can be achieved when compared with standard dc Magnetron Sputtering (dcMS) coating technology. Furthermore the capability of HIPIMS to produce a high quantity of ionized species can allow conformal coatings also for complex geometries. A study is under way at CERN to apply this technology for the Nb coating of SRF 1.3-1.5 GHz Cu cavities, and in parallel at SHU the plasma physics and its correlation with film morphology are being investigated. Recent results achieved with this technique are presented in the paper.

TUP081	Chemical Vapor Deposition Techniques for the Multilayer Coating of Superconducting RF Cavities	cavity, SRF, controls, experiment	635
	F. Weiss, C. Jimenez, S. Pignard Institut Polytechnique de Grenoble, Grenoble INP, Grenoble, France C.Z. Antoine CEA/IRFU, Gif-sur-Yvette, France M. Benz, E. Blanquet, R. Boichot, A. Mantoux, F. Mercier Laboratoire SIMAP, Grenoble-INP, CNRS, UJF, Saint Martin d'Hères, France
	Issued from the recent development of thin films technologies, multilayer nanostructures face today very challenging questions in materials science: ultimate size reduction, process control at an atomic scale, new size driven properties and system characterisation. For superconducting RF technologies a significant breakthrough could arise from the use of multilayered structures deposited inside Nb cavities. These multilayer nanostructures are based on the use of some 10 nanometers thick superconducting layers (d<λL) with a higher Tc than in Nb, alternating with insulating layers, required to decouple the superconducting films. We present here our first studies devoted to nano-layered superconductors produced by Chemical Deposition techniques: CVD and ALD. The basic principles of CVD and ALD will be presented together with new developments of the coordination chemistry for the ALD precursors, which is key point for the optimization of the individual layers. First results concerning NbN films obtained by CVD as well as CVD and ALD results concerning insulating materials used for Superconducting/insulating (S/I/S/I) multilayers structures will be reported.

TUP083	Film Deposition, Cryogenic RF Testing and Materials Analysis of a Nb/Cu Single Cell SRF Cavity	cavity, cryogenics, SRF, plasma	642
	X. Zhao JLab, Newport News, Virginia, USA R.L. Geng, Y.M. Li, A.D. Palczewski JLAB, Newport News, Virginia, USA Y.M. Li PKU, Beijing, People's Republic of China
	Funding: The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DEAC05- 06OR23177. In this study, we present preliminary results on using a cathodic-arc-discharge Nb plasma ion source to establish a Nb film-coated single-cell Cu cavity for SRF research. The polycrystalline Cu cavity was fabricated and mirror-surface-finished by a centrifugal barrel polishing (CBP) process at Jefferson Lab. Special pre-coating processes were conducted, in order to create a template-layer for follow-on Nb grain thickening. A sequence of cryogenic RF testing demonstrated that the Nb film does show superconductivity. But the quality factor of this Nb/Cu cavity is low as a result of high residual surface resistance. We are conducting a thorough materials characterization to explore if some microstructural defects or hydrogen impurities, led to such a low quality factor.

TUP085	Study of NbTi Welded Parts	cavity, laser, plasma, linac	659
	N. Bazin, C.Z. Antoine CEA/DSM/IRFU, France C. B. Baumier, G. Martinet IPN, Orsay, France F. F. Fortuna CSNSM, ORSAY CAMPUS, France J.-B. Sirven Commisariat à l'Energie Atomique (CEA/DEN/DPC), Direction de l'Energie Nucléaire, Gif-sur-Yvette, France
	Due to its properties, niobium-titanium alloy is widely used to manufacture the flanges of superconducting niobium accelerating cavities. The material hardness is compliant to provide UHV-tight connections with aluminum gaskets or spring-type gaskets (Helicoflex). And the alloy can be directly welded to the niobium. The paper will present the surface analysis made on NbTi samples after the chemical treatment and on a Nb / NbTi weld.

TUP086	Cryogen-Free RF System Studies Using Cryocooler-Cooled Magnesium Diboride-Coated Copper RF Cavities	cavity, cryomodule, SRF, accelerating-gradient	663
	A. Nassiri, R. Kustom, Th. Proslier ANL, Argonne, USA T. Tan, X. Xi TU, Philadelphia, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357. Studies on the application of magnesium diboride(MgB2)high-Tc superconducting films have shown promise for use with rf cavities. Studies are directed towards applying the films to niobium cavities with the goal to increase accelerating gradients to greater than 50 MeV/m. However, studies also have shown that MgB2 films, with a critical temperature over four times higher than Nb, have surface resistances equal, or nearly equal, at 8-12 K, to what is achieved with niobium at 4 K. It might be possible to design and operate cavity systems in the 8-12K temperature range with cryocoolers that are currently available. The current cryocoolers can remove as much as 20 watts per unit in the range of 8-12K. This suggests that helium-free superconducting RF systems are possible for future light sources and possible industrial and medical linear accelerators. Our current research is directed towards depositing MgB2 films onto copper, or other high thermal conductivity metal, substrates which would allow future cavities to be fabricated as film coated copper structures. We have started atomic layer deposition and Hybrid chemical vapor deposition studies of MgB2 on 2-inch copper coupons.

TUP087	RF Test Results of the first Nb3Sn Cavities Coated at Cornell	cavity, SRF, operation, linac	666
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As an alternative material to niobium for SRF cavities in particle accelerators, Nb3Sn presents two significant advantages. With a Tc of 18 K, it has a very small surface resistance at a given temperature, leading to a significant reduction in cryogenic costs; and with a predicted Hsh of nearly 400 mT, it has the potential to produce cavities with higher gradients and therefore shorter high energy linacs. Recently, two 1.3 GHz cavities have been fabricated and coated with Nb3Sn at Cornell. Tests of these first cavities have produced encouraging results, including a very high Tc and some very high-performing surface regions. These cavity results as well as new results of samples studied using TEM will be presented.

TUP097	Study of the Temperature Interface Between Niobium and Superfluid Helium. Temperature Waves Measurements from Heat Sources	cavity, SRF, factory, radio-frequency	700
	A. Ganshin, F. Furuta, D.L. Hartill, G.H. Hoffstaetter, K.M. Price, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431. One of the most important properties of Superconducting Radio Frequency (SRF) cavities is their ability to disperse generated heat from the internal cavity wall to the external super fluid helium bath. When the generated heat is not removed fast enough, an effect known as thermal feedback dominates, resulting in medium field Q-slope. This medium field Q-slope has the ability to reduce the Q factor should it become strong enough. To determine what physical factors affect the creation of the medium field Q-slope we will be computationally modeling the medium field Q-slope with varying parameters, such as Kapitza conductivity, wall thickness, RF frequency, bath temperature, residual resistivity ratio, residual resistance, and phonon mean path. Our results show that the medium-field Q slope is highly dependent on the Kapitza conductivity and that by doubling the Kapitza conductivity the medium field Q-slope reduces significantly. Understanding and controlling the medium ﬁeld Q-slope will benefit future continuous wave (CW) applications such as the Energy Recovery Linacs (ERL) where cryogenics costs dominate due to CW operation at medium ﬁelds (< 20 MV/m).

TUP100	Medium Field Q-Slope Studies in High Frequency Cavities	cavity, operation, superconductivity, factory	705
	O.S. Melnychuk, A. Grassellino, A.I. Sukhanov Fermilab, Batavia, USA
	A phenomenon of Medium Field Q-Slope (MFQS) in superconducting RF cavities is of high importance because it occurs in the field range (5-20MV/m) that includes designed operation fields of future CW accelerators. MFQS impacts resistive losses in the cavity and, consequently, directly affects accelerator operation costs. We present studies of MFQS based on vertical test data for 1.3GHz nine-cell cavities and make comparisons of vertical test data from different laboratories.

TUP108	Study on Niobium Scratch and Tantalum or Carbonaceous Contamination at Niobium Surface with Field Emission Scanner	cavity, electron, site, controls	731
	S. Kato, H. Hayano, T. Kubo, T. Noguchi, T. Saeki, M. Sawabe KEK, Ibaraki, Japan
	It is mandatory to investigate field emission from niobium SRF cavity surface systematically since even small field emission often limits the cavity performance terribly. The field emission strength and the number of emission sites strongly depend on niobium surface properties which are determined by its surface treatment and handling. It was found that carbonaceous contamination including carbon, oxygen, sometimes, nitrogen often segregates at CPed or EPed surface with a size of several micron to several tens of micron-meters. There is a strong doubt that this contamination causes field emission from the surface. Newly developed field emission scanner (FES) allows us to measure a distribution of the field emitting sites over a sample surface at a given field strength along with its SEM (scanning electron microscope) observation and EDX (energy dispersive x-ray) analysis. This article describes results of the FES-SEM-EDX application to carbonaceous contamination at niobium surface.

TUP110	An X-Ray Fluorescence Probe for Defect Detection in Superconducting 1.3 GHz Cavities	cavity, detector, embedded, radiation	736
	P. Michelato, M. Bertucci INFN/LASA, Segrate (MI), Italy A. Navitski, W. Singer, X. Singer DESY, Hamburg, Germany C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy Y. Tamashevich Uni HH, Hamburg, Germany
	The aim of this project is to develop a system for defect detection by means of X-ray fluorescence (XRF) analysis. XRF is a high sensitivity spectroscopy technique allowing the detection of trace element content, such as the few microgram impurities, responsible for low cavity performances if embedded in the equatorial region during cavity manufacturing. The proposed setup is customized on 1.3 GHz TESLA-type niobium cavities: both the detector and the X-ray excitation source are miniaturized so to allow the probe to enter within the 70 mm iris diameter and aside of the HOM couplers. The detection-excitation geometry is focused on cavity cell equator surface located at about 10³ mm from the cavity axis, with an intrinsic spot-size of about 10 mm. The measuring head will be settled on a high angular resolution optical inspection system at DESY, exploiting the experience of OBACHT. Defect position is obtained by means of angular inner cavity surface scanning. A quantitative determination of defect content can also be carried out by means of fundamental parameters technique with a Niobium standard calibration.

TUP111	Experimental Investigations of the Quench Phenomena for the Quench Localization by the Second Sound Wave Method	cavity, SRF, controls, experiment	739
	J. Plouin, J.-P. Charrier, C. Magne, J. Novo CEA/DSM/IRFU, France L. Maurice CEA/IRFU, Gif-sur-Yvette, France
	The quench localization by the second sound method is now widely used in many laboratories. This method avoids the complicated implementation of temperature arrays around the surface cavities. Instead, specific sensors are placed around the cavity and the time of arrival of the second sound wave generated by the quench is measured on each sensor; then the distance from sensors to quench is deducted from the theoretical second sound wave velocity. In principle, the quench position can be localized with a triangulation by a limited number of sensors. However, many measurements have shown that the time of arrival of the wave was not corresponding to the theoretical second sound wave velocity: the “measured” velocity is often 50% higher than the theory. At CEA-Saclay we performed several measurements on single cell cavities to investigate these phenomena. Several hypotheses are studied: large quench spot, heat propagation by another phenomenon than the second sound near to the cavity where the heat power density is very high. These results and the discussions on these hypotheses will be presented.

TUP112	Time-Resolved Measurements of High-Field Quench in SRF Cavities	cavity, SRF, simulation, accelerating-gradient	743
	S. Antipov University of Chicago, Chicago, Illinois, USA E. Efimenko MIPT, Dolgoprudniy, Moscow Region, Russia A. Romanenko, D.A. Sergatskov Fermilab, Batavia, USA
	Fermilab’s temperature mapping system for SRF cavities has been improved to observe quench dynamics with 1ms time resolution. The increase in sampling rate was achieved by localizing the quench and then performing the measurements using a limited subset of thermometers. Implemented experimental procedure allowed to measure temperature distribution within quench spot, as well as the amount of stored energy, at the moment quench starts, during its growth, and decay. For three tested SRF cavities, quenching at fields 21.7 – 33 MeV/m, maximal radius of the normal zone was 40 – 65 mm; time to return to superconducting state: 90 – 250 ms. In the beginning of the process temperature increase rate in the center of the normal zone is as high as 2.5 K/ms, radius increase rate – 20 mm/ms. The described experimental procedure can be useful for investigating how different surface treatments affect the breakdown, understanding of the nature of high-field quench, improvement of quench detection techniques, and material science research for future SRF cavities.

WEIOA03	Nb Sputtered Quarter Wave Resonators for the HIE-ISOLDE	cavity, cathode, vacuum, linac	767
	W. Venturini Delsolaro, S. Calatroni, A. D'Elia, B. Delaup, N.M. Jecklin, Y. Kadi, P. Maesen, I. Mondino, A. Sublet, M. Therasse CERN, Geneva, Switzerland A. D'Elia UMAN, Manchester, United Kingdom D.A. Franco Lespinasse, G. Keppel, V. Palmieri, S. Stark INFN/LNL, Legnaro (PD), Italy
	The HIE-ISOLDE superconducting linac will be based on quarter wave resonators (QWRs), made by Niobium sputtering on Copper. The operating frequency at 4.5 K is 101.28 MHz and the required performance for the high beta cavity is 6 MV/m accelerating field for 10 W maximum power dissipation. These challenging specifications were recently met at CERN at the end of a vigorous development program. The paper reports on the progress of the cavity RF performance with the evolution of the sputtering process; it equally illustrates the parallel R&D which is ongoing at CERN and at INFN in the quest for even higher performances.
	Slides WEIOA03 [14.564 MB]

WEIOA04	Nb3Sn for SRF Application	cavity, SRF, laser, vacuum	773
	M. Liepe, S. Posen Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The superconductor Nb3Sn is a promising alternative to standard niobium for SRF applications for two reasons: Its larger superconducting energy gap results in significantly lower BCS surface resistance at typical SRF operating temperatures. Additionally, theoretical predictions suggest that the maximum operating field of Nb3Sn cavities could be twice that of niobium cavities. Early work on a small number of Nb3Sn coated cavities indeed showed 2K to 4.2K quality factors well above what is achievable with niobium, though at accelerating fields below ~10 MV/m only. After many years of worldwide inactivity, Cornell has taken the lead and initiated a new R&D program on Nb3Sn to explore its full potential for SRF applications. New facilities for coating cavities with Nb3Sn have been set up at Cornell, and 1.3 GHz single cell cavities have been coated and tested. This talk presents the Cornell Nb3Sn program, discusses first promising results obtained, and also gives an overview of other Nb3Sn SRF work worldwide.
	Slides WEIOA04 [3.854 MB]

WEIOC01	High Resolution Surface Resistance Studies	quadrupole, cavity, shielding, superconductivity	785
	S. Aull, S. Döbert, T. Junginger CERN, Geneva, Switzerland S. Aull, J. Knobloch University of Siegen, Siegen, Germany J. Knobloch HZB, Berlin, Germany
	Funding: Work supported by the German Doctoral Students program of the Federal Ministry of Education and Research (BMBF). The attempt to reach quality factors beyond 10¹¹ and pushing the accelerating gradients of SRF cavities to the theoretical limit, the treatment depending loss mechanisms in niobium need better understanding. CERNs Quadrupole Resonator enables sub-nΩ-resolution measurements of the surface resistance. The available parameters cover resonant modes at 400, 800 and 1200 MHz, any temperature up to 15 K and rf fields up to 60 mT. Recently the setup has been extended with a coil creating a dc magnetic field for trapped flux studies. Overall, much more information about the rf performance is accessible compared to regular cavity measurements. Since the samples are flat disks of 75 mm diameter geometric fabrication issues are simplified which makes the Quadrupole Resonator also the perfect tool to study alternative materials or new coating techniques. In this contribution in depth studies of a heat treated bulk niobium sample exploiting the complete parameter range of the setup are presented.
	Slides WEIOC01 [2.724 MB]

WEIOC02	Multilayers Activities at Saclay / Orsay	cavity, SRF, vacuum, superconductivity	789
	C. B. Baumier, G. Martinet IPN, Orsay, France C.Z. Antoine CEA/IRFU, Gif-sur-Yvette, France F. F. Fortuna CSNSM, ORSAY CAMPUS, France J.C. Villegier CEA/INAC, Grenoble Cedex 9, France
	In the investigations on the high gradient SRF cavities, the superconducting multilayer is a promising alternative. The predictions show that an SIS (Superconductor/Isolator/Superconductor) nano-composite could improve the efficiency limited by the bulk Nb it-self used today for accelerating cavities. We start, at the IPNO lab in collaboration with the CSNSM lab (CNRS) and Irfu lab (CEA), an experimental study to test the screening effect on multilayer assemblies. Based on 3rd harmonic magnetometer and a TE011 SRF cavity, measurements of first critical magnetic field HC1 and surface resistance of samples have been performed. Along with these first results, we are starting the development of a MBE deposition. This set-up is devoted to optimise the best organisation of the multilayer to produce the model sample, and to find, in a close future, a realistic solution to apply this technique on an accelerating SRF cavity. Labex P2IO funding
	Slides WEIOC02 [3.035 MB]

WEIOC04	Theoretical Field Limits for Multi-Layer Superconductors	SRF, cavity, experiment, superconductivity	794
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA G. Catelani Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany J.P. Sethna Cornell University, Ithaca, New York, USA M.K. Transtrum M.D.A.C.C., Houston, Texas, USA
	With modern cavity preparation techniques, niobium SRF cavities reach surface magnetic fields very close to the fundamental limit of the superheating field of the material, and researchers are looking to alternative superconductors to sustain even higher fields. However, these materials may have an increased vulnerability to flux penetration at defects, even small ones, as a result of their short coherence lengths. A. Gurevich has proposed [1] a method of mitigating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the SRF community, to help researchers to optimize cavities made from alternative superconductors. [1] A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)
	Slides WEIOC04 [4.116 MB]

THIOA03	Cavity Fabrication Study in CFF at KEK	cavity, electron, HOM, gun	821
	M. Yamanaka, Y. Ajima, H. Inoue, T. Kubo, T. Saeki, Y. Watanabe, S. Yamaguchi KEK, Ibaraki, Japan
	The construction of new facility for the fabrication of superconducting RF cavity at KEK was completed in 2011. It is equipped with the following machines; an electron-beam welding (EBW) machine, a servo press machine and a CNC vertical lathe. A chemical etching apparatus is also equipped. The study on the fabrication of 9-cell cavity for International Linear Collier (ILC) has been started from 2009 using this facility. The study is focusing on the cost reduction with keeping high performance of cavity, and the goal is the establishment of mass-production procedure for ILC.
	Slides THIOA03 [7.823 MB]

THIOC01	Low Beta Cavity Development for an ATLAS Intensity Upgrade	cavity, cryomodule, linac, ion	850
	M.P. Kelly, Z.A. Conway, S.M. Gerbick, M. Kedzie, S.H. Kim, R.C. Murphy, B. Mustapha, P.N. Ostroumov, T. Reid ANL, Argonne, USA
	The set of seven new 72 MHz quarter wave SC (QWR) cavities has been completed and is being installed in the ATLAS heavy-ion accelerator at Argonne. The aim is to provide at least 17.5 MV accelerating potential with large acceptance and minimal beam losses for high intensity ion beams. The cavity electromagnetic design uses optimizations not used before with QWR including a large taper on both the inner and outer conductors in order to reduce surface fields and make efficient use of space along the beam line. Electropolishing (EP) on the finished cavities with integral helium jacket and no demountable RF joints has been performed, and is the first for any low beta SC cavity. This type of EP, adapted from Argonne systems for the linear collider effort, appears to have a large benefit in terms of the average quench field which range between 103-165 mT for five QWR tested to date. Cavity residual resistances at the proposed operating point of ~70 mT are low, clustering close to a value of ~2nOhm. Additional technical details including the almost exclusive use of wire EDM for niobium fabrication and a new CW 4 kW RF power coupler are presented.
	Slides THIOC01 [10.152 MB]

THIOD03	Cavity Development for the Linear IFMIF Prototype Accelerator	cavity, cryomodule, simulation, SRF	878
	N. Bazin, P. Carbonnier, G. Devanz, G. Disset, N. Grouas, P. Hardy, F. Orsini, D. Roudier CEA/DSM/IRFU, France J. Neyret CEA/IRFU, Gif-sur-Yvette, France
	The Linear IFMIF Prototype Accelerator (LIPAc), which is presently under design and realization, aims to accelerate a 125 mA deuteron beam up to 9 MeV. Therefore, a low-beta 175 MHz Half-Wave Resonator (HWR) was initially designed and manufactured with a tuning system based on a capacitive plunger located in the electric field region. Following the results of the vertical tests at 4.2K, this tuning system was abandoned and replaced by a conservative solution based on the HWR wall deformation using an external mechanical tuner. This paper will focus on the manufacturing of the prototype cavity, the studies realized to explain the first test results and the solutions taken to overcome the difficulties, leading to the validation of the prototype. Then, we will present the new cavity design.
	Slides THIOD03 [8.845 MB]

THP002	Design of 3-Cell Travelling Wave Cavity for High Gradient Test	cavity, accelerating-gradient, feedback, pick-up	892
	P.V. Avrakhov, A. Kanareykin, R.A. Kostin, Y. Xie Euclid TechLabs, LLC, Solon, Ohio, USA S. Kazakov, N. Solyak, V.P. Yakovlev Fermilab, Batavia, USA
	Utilization of a superconducting traveling wave accelerating (STWA) structure with small phase advance per cell for future high energy linear colliders may provide accelerating gradient 1.2/1.4 times larger [1] than standing wave structure. However, the STWA structure requires a feedback waveguide [1]. Recent tests of 1.3 GHz model of a single-cell cavity with waveguide feedback demonstrated an accelerating gradient comparable to the gradient in a single-cell ILC-type cavity from the same manufacturer [2]. In the present paper a design for a STWA resonator with a 3-cell accelerating cavity for high gradient tests is considered. Methods to create and support the traveling wave in this structure are discussed. The results of detailed studies of the mechanical and tuning properties of the superconducting resonator with 3-cell traveling wave accelerating structure are also presented.

THP011	Improving Gradient of 9-cell SRF Cavities at Peking University	cavity, SRF, accelerating-gradient, electron	914
	J.K. Hao, J.E. Chen, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, F. Wang, H.M. Xie, B.C. Zhang, K. Zhao, F. Zhu PKU, Beijing, People's Republic of China
	Four 9-cell TESLA superconducting cavities have been fabricated with Ningxia OTIC niobium material, including two fine grain and two large grain niobium cavities. The cavities have been tested after post treatments. At the early stage (PKU1 and PKU2), the gradient was about 23 MV/m. The gradient of PKU3 reached 28.4 MV/m, but the Q is low. The newest large grain 1.3 GHz 9-cell TESLA type SRF cavity (PKU4) has been made with careful control of machining, and improved surface treatment and electron beam welding. The maximum of gradient is 32.4 MV/m and the intrinsic quality factor (Q0) is 1.3x10¹⁰, which meet the requirement for ILC both in accelerating gradient and intrinsic quality factor.

THP016	DEVELOPMENT OF THE SUPERCONDUCTING HALF WAVE RESONATOR FOR INJECTOR II IN C-ADS	cavity, simulation, linac, proton	923
	W.M. Yue, W. Chang, S. He, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, F.F. Wang, R.X. Wang, M.X. Xu, C. Zhang, S.H. Zhang, S.X. Zhang IMP, Lanzhou, People's Republic of China
	The Development of the Half Wave Resonator (HWR010) is based on the China ADS. The HWR010 operates at 162.5 MHz and can provide more than 0.78 MV of accelerating voltage per cavity for proton withβopt=0.10. We have designed the HWR010 in 2011. A copper model has been fabricated to test the HWR fabrication procedure. Five HWR010s have been fabricated in 2012. The HWR010s has finished the vertical testing and the Q0 is 4·10⁸ at Epeak = 45 MeV/m, and one of the HWR010s has been vertical tested with helium vessel. The slow tuner and high power coupler for this HWR have been developed and tested.

THP022	DEVELOPMENT OF A VERY LOW BETA SUPERCONDUCTING SINGLE SPOKE CAVITY FOR CHINA-ADS LINAC*	cavity, accelerating-gradient, linac, LLRF	942
	H. Li, J.P. Dai, L.H. Li, H.Y. Lin, Q. Ma, W.M. Pan, Y. Sun, Q.Y. Wang, J. Zhang IHEP, Beijing, People's Republic of China H. Huang, P. Sha Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
	Twelve very low Beta superconducting single spoke cavities whose Beta is only 0.12 (Spoke012) operating at 325MHz, are adopted in Injector I for China-ADS linac. This type of spoke cavity is believed to be one of the key challenges for its very low geometric Beta. So far, collaborated with Peking University and Harbin Institute of Technology, IHEP has designed, fabricated and tested the spoke012 prototype cavity successfully. This paper presents the details of the design, fabrication and vertical test results for Spoke012 prototype cavity.

THP030	Superconducting RF Cavity Development With UK Industry	cavity, SRF, multipactoring, accelerating-gradient	966
	A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C.A. Cooper, C.M. Ginsburg, A. Grassellino, O.S. Melnychuk, A.M. Rowe, D.A. Sergatskov Fermilab, Batavia, USA J.R. Everard, N. Shakespeare Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
	As part of a continuing STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures Daresbury Laboratory and Shakespeare Engineering Ltd are developing the capability to fabricate, process and test a niobium 9-cell 1.3 GHz superconducting RF cavity. A single-cell cavity fabricated under this grant was surface processed and tested at Fermilab, and achieved an accelerating gradient in excess of 40 MV/m at an unloaded quality factor in excess of 1.0 x 10¹⁰. This paper presents the results of the single-cell cavity testing and discusses the progress made to date in the development of the design and manufacture of a 9-cell niobium cavity, which Shakespeare Engineering Ltd will fabricate and which is anticipated to be qualified in 2014.

THP038	Development and Performance of a High Field TE-Mode Sample Host Cavity	cavity, simulation, resonance, SRF	985
	D.L. Hall, M. Liepe, I.S. Madjarov, K.P. McDermott, N.R.A. Valles Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: US National Science Foundation Career award PHY-0841213 A TE-mode 4 GHz sample host cavity has been designed and constructed at Cornell for the purpose of testing wafers of niobium and other candidates for the construction of SRF cavities. Simulations made using CLANS and ACE3P indicate that the peak magnetic field on the sample plate will reach approximately 120 mT before a quench occurs on the surface of the cavity due to thermal runaway. This quench field can be further increased using a 1400 C treatment to improve the thermal conductivity of the niobium bulk and a 120 C treatment to minimise the BCS surface resistance of the cavity walls. Such an improvement would put peak fields of 170 mT within reach of this cavity. Results of the cavity design, fabrication and first vertical test are presented and discussed. *Development of Superconducting RF Sample Host Cavities and study of Pit-Induced Cavity Quench, Yie Xie, PhD Thesis, Cornell University, Jan 2013

THP084	The Tuning System for the HIE-ISOLDE High-Beta Quarter Wave Resonator	cavity, simulation, controls, LLRF	1121
	P. Zhang, L. Alberty, L. Arnaudon, K. Artoos, S. Calatroni, O. Capatina, A. D'Elia, Y. Kadi, I. Mondino, T. Renaglia, D. Valuch, W. Venturini Delsolaro CERN, Geneva, Switzerland A. D'Elia UMAN, Manchester, United Kingdom
	Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI. A new linac using superconducting quarter-wave resonators (QWR) is under construction at CERN in the framework of the HIE-ISOLDE project. The QWRs are made by Niobium sputtered on a bulk Copper substrate. The working frequency at 4.5 K is 101.28 MHz and they will provide 6 MV/m accelerating gradient on the beam axis with a total maximum power dissipation of 10 W on cavity walls. A tuning system is required in order to both minimize the forward power variation in beam operation and to compensate the unavoidable uncertainties in the frequency shift during the cool-down process. The tuning system has to fulfill a complex combination of RF, structural and thermal requirements. The paper presents the functional specifications and details the tuning system RF and mechanical design and simulations. The results of the tests performed on a prototype system are discussed and the industrialization strategy is presented in view of final production.

FRIOA03	Fabrication and Testing of Deflecting Cavities for APS	cavity, operation, coupling, SRF	1170
	J.D. Mammosser JLab, Newport News, Virginia, USA P. Dhakal, J. Henry, R.A. Rimmer, H. Wang, K.M. Wilson JLAB, Newport News, Virginia, USA J.F. Fuerst, J.P. Holzbauer, J.S. Kerby, A. Nassiri, G.J. Waldschmidt, G. Wu, Y. Yang ANL, Argonne, USA F. He PKU, Beijing, People's Republic of China Z. Li SLAC, Menlo Park, California, USA
	Abstract Jefferson Lab in Newport News, Virginia, in collaboration with Argonne National Laboratory, Argonne, Il, has fabricated and tested three production, 2.815 GHz crab cavities for Argonne’s Short-Pulse X-ray project. These cavities are unique in that the cavity and waveguides were milled from bulk large grain niobium ingot material directly from 3D CAD files. No forming of sub components was used with the exception of the beam-pipes. The cavity and helium vessel design along with the RF performance requirements makes this project extremely challenging for fabrication. Production challenges and fabrication techniques as well as testing results will be discussed in this paper.
	Slides FRIOA03 [22.677 MB]

FRIOB02	Development and Performance of 325 MHz Single Spoke Resonators for Project X	cavity, operation, vacuum, electron	1187
	L. Ristori, M.H. Awida, P. Berrutti, C.M. Ginsburg, I.V. Gonin, T.N. Khabiboulline, M. Merio, T.H. Nicol, D. Passarelli, A.M. Rowe, D.A. Sergatskov, A.I. Sukhanov, V.P. Yakovlev Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. Two types of single spoke resonators will be utilized for beam-acceleration in the low energy part of the Project X linac. SSR1 and SSR2 operate at 325 MHz and at an optimal beta of 0.22 and 0.51 respectively. After the initial phase of prototyping, a production run of 10 SSR1 resonators was recently completed in US industry. The qualification of this group of resonators in the Fermilab VTS is proceeding successfully and nearly complete. The first qualified resonator has been outfitted with a Stainless Steel helium vessel. Preliminary test results for the first jacketed SSR1 are presented. The first RF power couplers were ordered, the design of the double-lever tuning mechanism is almost complete.
	Slides FRIOB02 [8.800 MB]

FRIOB04	CERN Developments for 704 MHz Superconducting Cavities	cavity, operation, linac, proton	1198
	O. Capatina, G. Arnau-Izquierdo, S. Atieh, I. Aviles Santillana, R. Bonomi, S. Calatroni, J.K. Chambrillon, R. Garoby, F. Gerigk, M. Guinchard, T. Junginger, M. Malabaila, L. Marques Antunes Ferreira, S. Mikulas, V. Parma, T. Renaglia, K.M. Schirm, T. Tardy, M. Therasse, A. Vacca, N. Valverde Alonso, A. Vande Craen CERN, Geneva, Switzerland F. Pillon Kraftanlagen Nukleartechnik GmbH, Heidelberg, Germany
	The Superconducting Proton Linac (SPL) is an R&D effort coordinated by CERN in partnership with other international laboratories. It is aiming at developing key technologies for the construction of a multi-megawatt proton linac based on state-of-the-art RF superconducting technology, which would serve as a driver in new physics facilities for neutrinos and/or Radioactive Ion Beam (RIB). Amongst the main objectives of this R&D effort, is the development of 704 MHz bulk niobium β=1 elliptical cavities, operating at 2 K with a maximum accelerating gradient of 25 MV/m, and the testing of a string of cavities integrated in a machine-type cryomodule. The cavity together with its helium tank had to be carefully designed in coherence with the innovative design of the cryomodule. New fabrication methods have also been explored. Five such niobium cavities and two copper cavities are in fabrication. The key design aspects are discussed, the results of the alternative fabrication methods presented and the status of the cavity manufacturing and surface preparation is detailed.
	Slides FRIOB04 [8.677 MB]

FRIOC01	Design of the 352 MHz, Beta 0.50, Double-Spoke Cavity for ESS	cavity, cryomodule, simulation, operation	1212
	P. Duchesne, S. Bousson, S. Brault, P. Duthil, G. Olry, D. Reynet IPN, Orsay, France S. Molloy ESS, Lund, Sweden
	The ESS proton accelerator contains a superconducting sector consisting in three families of superconducting radiofrequency (SRF) bulk niobium cavities, operating at a nominal temperature of 2K: a family of Spoke cavities for the medium energy section followed by two families of elliptical cavities for higher energies. The superconducting Spoke section, having a length of 58.6m, consists of 14 cryomodules, each of them housing two 352.2 MHz β=0.50 Double-Spoke Resonators (DSR). The operating accelerating field is 8MV/m. The choice of the Spoke technology is guided by the high performances of such structures. Benefitting from 10 years of extensive R&D experience carried out at IPNO, the electromagnetic design studies came out with a solution that fulfills requirements of beam dynamics analysis and manufacturing considerations. Pursuing the same objective, the mechanical design of the cavity and its helium vessel were optimized by performing intensive coupled RF-mechanical simulations. We propose to present a review of the RF and mechanical design studies of the Spoke cavity. We will conclude with the integration of the Spoke cavity with its ancillaries inside the cryomodule.
	Slides FRIOC01 [6.321 MB]

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MOIOA03

The Challenge and Realization of the Cavity Production and Treatment in Industry for the European XFEL

cavity, controls, superconductivity, HOM

18

W. Singer, J. Iversen, A. Matheisen, H. Weise
DESY, Hamburg, Germany
P. Michelato
INFN/LASA, Segrate (MI), Italy

The main effort in production of 1.3 GHz cavities for the EXFEL was dedicated to transfer the superconducting technology to the industry. These know how transfer is executed by DESY and INFN/LASA team. The preparation phase based on prototype cavities covered: qualification of potential vendors for material and cavity fabrication; work out recipe and strategy for qualification of the infrastructure for cavity surface treatment at industry; definition of the quality management strategy, documentation and electronically data exchange. Production of 800 series cavities on the principle “build to print” is contracted to companies Research Instruments and Ettore Zanon. High purity niobium and NbTi for resonators provides DESY. The principles of the material and cavities production in conformity with European Pressure Equipment Directive are developed together with the notified body. New or upgraded infrastructure has been established at both companies. The first several tens of series cavities have been produced and treated. Most of the cavities handed over to DESY up to now fulfill immediately the EXFEL specifications. The cavity production for EXFEL will be finished mid of 2015.

Slides MOIOA03 [7.394 MB]

MOIOC01

Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities

cavity, interface, coupling, operation

57

V. Palmieri
INFN/LNL, Legnaro (PD), Italy

Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.

Slides MOIOC01 [15.558 MB]

MOIOC02

A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor

cavity, impedance, electron, superconductivity

63

B. P. Xiao, C.E. Reece
JLab, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: This manuscript has been authored in part by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
There is a need to understand the intrinsic limit of RF surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors, based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and Fermi Lab with carefully prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.

Slides MOIOC02 [3.122 MB]

MOP032

Statistic to Eddy-Current Scanning of Niobium Sheets for European XFEL

cavity, controls, survey, superconducting-RF

171

A. Brinkmann, S. Arnold, A. Ermakov, J. Iversen, M. Lengkeit, A. Poerschmann, L. Schaefer, W. Singer, X. Singer
DESY, Hamburg, Germany

The fabrication experiences of superconducting cavities for FLASH have shown that eddy-current scanning of the Nb-sheets foreseen for half-cells reduces the cavity failures. New eddy current devices have been developed and build together with the industry for the production of 800 pieces 1.3 GHz superconducting niobium cavities for European XFEL. More than 15.000 Nb-sheets provided by three companies have been tested by eddy-current scanning. The sheets that demonstrated local deviations of the signal have been subsequently non-destructively examined by 3d-microscope and X-Ray element analysis. The surface defects (dents, holes, scratches) are the mainly detected flaws. In addition several types of foreign material inclusions observed. Statistic concerning eddy-current signal deviation and rejection rates for each supplier will be presented.

MOP033

Quality Assurance and Acceptance Testing of Niobium Material for Use in the Construction of the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU)

cavity, linac, SRF, controls

174

C. Compton, D. Miller
FRIB, East Lansing, USA
T.R. Bieler, D. Kang
Michigan State University, East Lansing, USA
S.K. Chandrasekaran, N.T. Wright
MSU, East Lansing, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University
Niobium is the current material of choice for the fabrication of superconducting radio frequency (SRF) cavities used in SRF based accelerators. Although niobium specifications for this application have been well established, material properties of as-received materials can still vary substantially. As required for the FRIB accelerator, large volumes (60,000 lbs) of niobium materials (sheet, tube, and flange) have been contracted to several niobium vendors. The FRIB cavity designs require very large niobium sheets, increasing the difficulty in fabrication and potential for contamination. FRIB has developed and initiated plans to control niobium specifications and perform incoming acceptance checks to ensure quality is maintained. Acceptance results from the first niobium shipment will be presented, looking at several production lots from the same vendor and across multiple vendors. Non-conforming results were observed and will be discussed including follow-up investigations and mitigation strategies to improve quality of future shipments.

MOP034

The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON

cavity, target, controls, accelerating-gradient

180

A. Gresele, M. Giaretta, A. Visentin
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
A.A. Sulimov, J.H. Thie
DESY, Hamburg, Germany

Serial production of superconducting cavities for European-XFEL was successfully started at E.ZANON at the end of last year. The production rate (3-4 cavities a week) allows us to summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed. The last results of new preparation cycles development in the frame of E-XFEL projects is also included

MOP035

Using an Engineering Data Management System for Series Cavity Production for the European XFEL

cavity, controls, database, data-management

183

J. Iversen, A. Brinkmann, J.A. Dammann, A. Poerschmann, W. Singer, J.H. Thie
DESY, Hamburg, Germany

For series production of 800 superconducting cavities for the European XFEL an Engineering Data Management System (EDMS) is in use as a tool for quality control and quality assurance. DESY is responsible for “in-time” supply of more than 24000 semi-finished products of niobium and niobium-titanium alloy. The EDMS as a main repository was set up to fulfill logistic requirements and to guarantee traceability and documentation issues according to the European pressure equipment directive (PED 97/23 EC). The main aspects consist of complete paperless documentation, fully automated transfer of quality management documents and data from vendor system to DESY’s EDMS, providing to industry an access to relevant documentation and processing of release procedures for acceptance levels and non-conformity reporting. A summary of documentation methods, procedures and first experiences will be presented.

MOP036

New Technique and Result of Laser Welded SCRF Cavity Developed at RRCAT

cavity, laser, vacuum, experiment

186

P. Khare, R. Arya, J. Dwivedi, R. Ghosh, G. Gilankar, C. Gupta, P.D. Gupta, A. Jain, S.C. Joshi, G.V. Kane, R. Kaul, P.K. Kush, G. Mundra, S.M. Oak, C.K. Pithawa, P. Ram Sankar, S.B. Roy, V.C. Sahni, R.S. Sandha, P. Shrivastava, B.N. Upadhyay
RRCAT, Indore (M.P.), India
C.A. Cooper, C.M. Ginsburg, A. Grassellino, C.S. Mishra, A.M. Rowe
Fermilab, Batavia, USA

A new technique to fabricate SCRF cavities with the help of laser welding process has been developed at Raja Ramanna Centre for Advanced Technology RRCAT), Indore, Department of Atomic Energy, India. In this technique, a pulsed Nd:YAG laser has been used and welding was performed in inert gas environment, in a specially designed welding rig. The advantages of this technique are reduced cost, small heat affected zone, no necessity to weld in vacuum and enhanced rate of production. The paper describes the technique and fabrication method of a single-cell 1.3 GHz SCRF cavity which was fabricated at RRCAT with this new technique. It also discusses the test result of this cavity which was processed and tested at Fermilab. The cavity reached an Eacc of 17MV/m with a Q0 of 1.4 E +10 at 2K. The cavity is being barrel polished for further improvement.

MOP038

Series Production of EXFEL 1.3 GHz SRF Cavities at E. Zanon: Management, Infrastructures and Quality Control

cavity, SRF, controls, cryogenics

194

G. Massaro
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
G. Corniani, M. Festa, M. Maule
Ettore Zanon S.p.A., Schio, Italy

In this paper we report on the capability of Ettore Zanon S.p.A. (EZ) to implement a EXFEL 1,3 GHz SRF cavities production system. In order to assure the series efficient repeatability of the product, this system is based on work team, composed of people with different skills, qualified infrastructures and technical procedures. A detailed study of the different work phases of the production cycle has been performed in advance, highlighting the technical difficulties and the production constraints. Based on this result, infrastructures and processes have been optimized to grant the specified quality and time/cost requirements and procedures and operating instructions, where the most complexes and delicate phases as well as the responsibilities and acceptance criteria are investigated, have been introduced. Qualification operations and eight pre-series cavities have proven EZ capability of fulfilling the imposed requirements. The above described manufacturing system allows nowadays a production rate of 4 cavities per week. EZ future developments involve minimizing time and costs while keeping the highest quality standard.

MOP045

Electropolishing for EXFEL Cavities Production at Ettore Zanon SpA

cavity, controls, cathode, superconductivity

220

M. Rizzi
Ettore Zanon S.p.A., Schio, Italy
A. Gresele
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
A. Matheisen, N. Steinhau Kühl
DESY, Hamburg, Germany
P. Michelato
INFN/LASA, Segrate (MI), Italy

A new horizontal electropolishing (EP) facility has been implemented by Ettore Zanon SpA for the series production of the EXFEL cavities produced by the company. According to EXFEL specification a bulk EP of at least 100 micron is the first step of the surface treatment for high performances. Particular attention has been dedicated to find the best configuration during qualification of the system. Correlation between process variables, RF tests at room temperature at Zanon and vertical RF tests at 2 K at DESY have been investigated and the Niobium removal optimized. The facility has been designed for industrial scope, in order to guarantee the required quality and production rate of 4 cavities per week. One of the most important aspects has been the system automation to have complete control of the process.

MOP048

PED Requirements Applied to the Cavity and Helium Tank Manufacturing

cavity, linac, controls, operation

227

A. Schmidt, J. Iversen, A. Matheisen, W. Singer
DESY, Hamburg, Germany

For the European XFEL more than 800 Cavities are manufactured by industrial partners. Each cavity is housed in an individual cryo vessel, the so called helium tank. All vessels are made from titanium and manufactured by industry as well. The cavity, welded into its helium tank, is a pressure loaded part and has to follow the pressure equipment directive - PED (97/23/EC). Setting up a series production of cavities and helium tanks by different vendors according given standards, was the task of the EXFEL WPG-1 LINAC-WP04. In cooperation with the TUEV-Nord as the notified body, DESY is responsible for the qualification of design, material in use and reasonable tests to get a certificate for pressure bearing parts.

MOP062

Production of 500 MHz SRF Modules the KEKB-type for Taiwan Photon Source

SRF, cavity, operation, vacuum

263

Ch. Wang, L.-H. Chang, M.H. Chang, L.J. Chen, F.-T. Chung, M.-C. Lin, Y.-H. Lin, Z.K. Liu, C.H. Lo, M.H. Tsai, T.-T. Yang, M.-S. Yeh, T.-C. Yu
NSRRC, Hsinchu, Taiwan
T. Furuya, K. Hara, T. Honma, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Nishiwaki, S. Takano
KEK, Ibaraki, Japan
F. Inoue, K. Sennyu, T. Yanagisawa
MHI, Hiroshima, Japan

The KEKB-type single-cell 500-MHz superconducting radio frequency (SRF) modules have been selected to power the 3 GeV, 500 mA, storage ring of the constructing Taiwan Photon Source (TPS) at National Synchrotron Radiation Research Center (NSRRC). The design target is to routinely deliver RF forward power up to 300 kW, CW, to single SRF module with highly reliable operation. Three sets of SRF modules have been successfully produced under a tight collaboration with High Energy Accelerator Research Organization (KEK) and Mitsubishi Heavy Industries Ltd. (MHI), after obtaining the technology transfer from KEK. MHI is responsible for the mechanical fabrication and cryo-module assembly, KEK for the surface and RF treatments of the niobium cavities, high power input couplers and HOM dampers and for the liquid-helium tests of the cryo-modules, and NSRRC for the electronic/diagnostic system, final assembly and system integration, high power horizontal test, and reliable test. This work reports the results obtained during the production of these three SRF modules at KEK and NSRRC.

MOP066

Development of Compact Cryomodules Housing HWRs for High-intensity SC CW Linacs

cavity, cryomodule, linac, proton

277

P.N. Ostroumov, Z.A. Conway, S.M. Gerbick, M. Kedzie, M.P. Kelly, S.H. Kim, S.V. Kutsaev, R.C. Murphy, B. Mustapha, T. Reid
ANL, Argonne, USA
D. Berkovits
Soreq NRC, Yavne, Israel
S. Nagaitsev
Fermilab, Batavia, USA

Funding: This work was supported by the U.S. Department of Energy, under Contracts No. DE-AC02-06CH11357, DE-AC02-76CH03000 and ANL WFO No. 85Y47.
Acceleration of high-intensity light-ion beams immediately after an RFQ requires a compact accelerating and focusing lattice with a high packing factor. We have developed a cryomodule which satisfies this requirement with eight accelerating-focusing periods for Project X at FNAL. Each focusing period consist of a 162.5-MHz SC HWR, a SC solenoid and a beam position monitor. The highly optimized EM parameters of the cavity were achieved by using double conical, hour glass like, inner and outer conductors. This design is also favorable for the beam dynamics because the short focusing periods which helps to better control the beam quality. All sub-systems of the cryomodule, except the vacuum-vessel, are in advanced stages of prototyping and testing. A similar concept has been developed for the design of several cryomodules for a 20 MeV/u proton/deuteron 200 kW linac at SNRC. These cryomodules house two types of 176 MHz half-wave resonators and require only modest modifications for the application. This paper will discuss the status of the FNAL cryomodule design and sub-system fabrication and its impact on future HWR cryomodule such as the SNRC project.

MOP070

Results on Quality Factors of 1.3 GHz Nine-Cell Cavities at DESY

cavity, factory, operation, linear-collider

297

F. Schlander
IKP, Mainz, Germany
F. Schlander
DESY, Hamburg, Germany

Superconducting cavities made of niobium are the basis of many particle accelerators around the world. Besides the quest for high accelerating fields for projects like European XFEL and the International Linear Collider, the quality factor, a measure for the resistance and hence the ohmic losses, is of importance, as it eventually determines the cryoplant size and its costs of operation. Especially for accelerators operating in continuous wave mode, the dynamic heat load generated by cavity operation exceeds the static heat load by far and thus requires minimisation. To investigate the current quality factor performance of 1.3 GHz cavities at DESY, the test results of some 50 recent cavities with state-of-the-art treatment have been examined regarding surface treatment and material.

Slides MOP070 [0.590 MB]

MOP073

IHEP 1.3 GHz Low Loss Large Grain 9-cell Cavity Fabrication, Processing and Test

cavity, HOM, SRF, vacuum

305

J.Y. Zhai, J. Gao, S. Jin, Z.Q. Li, Y. Liu, Z.C. Liu, Z.H. Mi, X.H. Peng, T.X. Zhao, H.J. Zheng
IHEP, Beijing, People's Republic of China
C.A. Cooper, C.M. Ginsburg, T.N. Khabiboulline, A.M. Rowe, D.A. Sergatskov
Fermilab, Batavia, USA
J.X. Wang, H. Yu, H. Yuan
BIAM, Beijing, People's Republic of China

The combination of the low-loss shape and large grain niobium material is expected to be the possible way to achieve higher gradient and lower cost for ILC 9-cell cavities, and will be essential for the ILC 1 TeV upgrade. As the key component of the “IHEP 1.3 GHz SRF Accelerating Unit Project”, a low-loss shape 9-cell cavity with full end groups using Ningxia large grain niobium (IHEP-02) was fabricated at IHEP in 2012. The cavity was processed (CBP and EP) and tested at FNAL. The cavity processing,test performance and gradient limitation is reported in this paper. We will weld the helium vessel, assemble the magnetic shield and install the cavity to IHEP ILC-TC1 cryomodule.

TUIOA01

Influence of the Couldown at the Transition Temperature on the SRF Cavity Quality Factor

cavity, shielding, SRF, experiment

370

O. Kugeler, J. Knobloch, J.M. Vogt
HZB, Berlin, Germany

The quality factor Q0 that can be obtained in a superconducting cavity is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We believe that cooling conditions have an additional impact, as they appear to influence the amount of trapped flux and hence the residual resistance. We constructed a test stand using a niobium rod shorted out by a titanium rod to mimic a cavity in its helium tank to study flux trapping. Here we can precisely control the temperature and measure the dynamics of flux trapping at the superconducting phase transition. We learned that magnetic flux can be generated when a temperature gradient exists along the rod and when the niobium transitions into the superconducting state it subsequently remains trapped. Furthermore, it was shown that the cooling rate during isothermal cooldown through the transition temperature can influence the amount of externally applied flux which remains trapped. The acquired knowledge may be used to modify the cooldown procedure of SRF cavities leading to a reduced level of trapped flux and hence operation closer to the BCS limit.

Slides TUIOA01 [1.276 MB]

TUIOA02

High Q0 Research: The Dynamics of Flux Trapping in Superconducting Niobium

cavity, experiment, simulation, shielding

374

J.M. Vogt
HZB, Berlin, Germany
J. Knobloch, O. Kugeler
BESSY GmbH, Berlin, Germany

The quality factor Q0 that can be obtained in a superconducting cavity is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We believe that cooling conditions have an additional impact, as they appear to influence the amount of trapped flux and hence the residual resistance. We have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and measure the dynamics of flux trapping at the superconducting phase transition. We learned that magnetic flux can be generated when a temperature gradient exists along the rod as the niobium transitions to the superconducting state, which subsequently remains trapped. It was also shown that the cooling rate can influence the amount of externally applied flux which is trapped. Furthermore, we also were able to demonstrate that flux lines become mobile if the superconductor is warmed close to below Tc. The acquired knowledge may be used to modify the cooldown procedure of SRF cavities leading to a reduced level of trapped flux and hence operation closer to the BCS limit.

Slides TUIOA02 [5.774 MB]

TUIOA05

New Insights Into Quench Caused by Surface Pits in SRF Cavities

cavity, laser, SRF, feedback

378

Y. Xie, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work supported by NSF Career award PHY-0841213 and the Alfred P. Sloan Foundation.
Surface defects such as pits have been identified as some of the main sources of limitations of srf cavity performance. A single cell cavity with 30 artificial pits in the high magnetic field region was made to gain new insight in how pits limit the cavity performance*. The test of the pit cavity showed clear evidence that the edges of two of the largest radius pits transitioned into the normal conducting state at field just below the quench field of the cavity, and that the quench was indeed induced by these two pits. The pit geometrical information measured by laser confocal microscopy combined with a numerical finite element ring-type defect model will be compared with temperature mapping results. Insights about quench and non-linear rf resistances will be presented.
*Y. Xie, PhD thesis, Cornell University, 2013

Slides TUIOA05 [3.101 MB]

TUIOB01

R&D Progress in SRF Surface Preparation With Centrifugal Barrel Polishing (CBP) for both Nb and Cu

cavity, SRF, synchrotron, experiment

398

A.D. Palczewski
JLAB, Newport News, Virginia, USA
B. Bullock
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
C.A. Cooper
Fermilab, Batavia, USA
S.C. Joshi
RRCAT, Indore (M.P.), India
A. Navitski
DESY, Hamburg, Germany
A.A. Rossi
INFN/LNL, Legnaro (PD), Italy

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Centrifugal Barrel polishing (CBP) is becoming a common R&D tool for SRF cavity preparation around the word. During the CBP process a cylindrically symmetric SRF cavity is filled with relatively cheap and environmentally friendly abrasive and sealed. The cavity is then spun around the cylindrical axis at high speeds uniformly conditioning the inner surface. This uniformity is especially relevant for SRF application because many times a single manufacturing defects limits cavity’s performance well below it’s theoretical limit. In addition CBP has created surfaces with roughness’s on the order of 10’s of nm which create a unique surface for wet chemistry or thin film deposition. CBP is now being utilized at Jefferson Laboratory, Fermi Laboratory and Cornell University in the US, Ko Enerugi Kasokuki Kenkyu Kiku in Japan, Deutsches Elektronen-Synchrotron in Germany, Laboratori Nazionali di Legnaro in Italy, and Raja Ramanna Centre for Advanced Technology in India. In this talk we will present current CBP research from each lab including polishing recipes, equipment, post CBP chemistry/heat treatment, and subsequent cryogenic cavity tests on niobium as well as copper cavities.

Slides TUIOB01 [2.204 MB]

TUIOC02

Bipolar EP: Electropolishing without Fluorine in a Water Based Electrolyte

cavity, SRF, experiment, controls

404

A.M. Rowe, A. Grassellino
Fermilab, Batavia, USA
T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, USA

Funding: Operated by Fermi Research Alliance, LLC under contract No. De-AC02-07CH11359 with the United States Department of Energy
For more than thirty years, preparing superconducting RF cavities for high performance has required the use of dangerous and ecologically damaging chemicals. Reducing the personnel and environmental risks associated with using these chemicals is a priority at Fermilab. Therefore, Fermilab pursued a project to adapt a non-hazardous and relatively benign bipolar electropolishing technique to SRF cavities that Faraday Technology, Inc. developed. Faraday initially developed this electropolishing technique to polish metal alloys used in automotive and semiconductor components as well as medical devices and implants. By modifying the cathodic/anodic interaction via a pulse forward/pulse reverse technique, Fermilab and Faraday Technology demonstrate the capability to polish 1.3 GHz single-cell cavities utilizing an aqueous 10% sulfuric acid electrolyte. We present the development of bipolar EP for single-cell 1.3 GHz cavities and show the results from vertical tests achieving gradients greater than 40 MV/m.

Slides TUIOC02 [1.251 MB]

TUIOC03

Fluorine Free Ionic Liquid Electropolishing of Niobium Cavities

cavity, cathode, experiment, superconductivity

410

V.B. Pastushenko, O.V. Malkova, V. Palmieri, A.A. Rossi, F. Stivanello, G. Yu
INFN/LNL, Legnaro (PD), Italy
G. Yu
CIAE, Beijing, People's Republic of China

Ionic liquids are an emerging breakthrough in green chemistry since the years 2000. In 2006, INFN-LNL was the first to apply a mixture of Choline Chloride and Urea to Niobium electropolishing. It was found that mirror like surfaces could be obtained at temperature higher than 120°C, with high throwing power. Subsequently the process was successfully applied to the electropolishing of a 6 GHz monocell cavity with the addition of sulphamic acid. In this work, we will report an intense investigation of the possible variants of the original recipe. We studied the influence on Niobium surface roughness of several parameters such as: other sulphamic, ammonium and carboxylic containing additives different than sulfamic acid, the possible substitution of Urea with ethylene glycol and malic acid, the current regime; the electrolyte temperature and the cathode shape, rotating horizontal electropolishing versus vertical electropolishing. Due to the cavity hollow cylindrical shape, the electrolyte temperature appeared to be the most crucial parameters among those above mentioned for a uniform dissolution of niobium.

Slides TUIOC03 [14.464 MB]

TUIOC04

Analysis of Post-Wet-Chemistry Heat Treatment Effects on Nb SRF Surface Resistance

cavity, SRF, superconductivity, site

414

P. Dhakal, G. Ciovati, P. Kneisel, G.R. Myneni
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Most of the current R&D in SRF is focused on ways to reduce the construction and operating cost of SRF-based accelerators as well as on the development of new or improved cavity processing techniques. The increase in quality factors is the result of the reduction of the surface resistance of the materials. A recent test [*] on a 1.5 GHz single cell cavity made from ingot niobium of medium purity and heat treated at 1400 C in a ultra-high vacuum induction furnace resulted in a residual resistance of ~ 1nanoohm and a quality factor increasing with field up to ~ 5×10¹⁰ at a peak magnetic field of 90 mT. In this contribution, we present some results on the investigation of the origin of the extended Q0-increase, obtained by multiple HF rinses, oxypolishing and heat treatment of “all Nb” cavities.
[*] P. Dhakal et al., Phys. Rev. ST Accel. Beams 16, 042001 (2013).

Slides TUIOC04 [4.838 MB]

TUIOC05

Purification of 6 GHz Cavities by Induction Heating

cavity, induction, vacuum, SRF

419

A.A. Rossi, A. Battistello, M. Checchin, V. Palmieri, S. Stark, F. Stivanello, R.K. Thakur, G. Yu
INFN/LNL, Legnaro (PD), Italy

We have developed an innovative technique for purification of bulk-Nb 6GHz RF cavities under ultra-high vacuum (UHV) system. The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect statistics of surface treatments and RF test. Cavities are RF tested before and after high temperature treatment under UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher than 2000°C and close to the melting point of Nb for less than a minute while few seconds at maximum temperature. Before RF test and UHV annealing, the surface treatment processes like tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high pressure rinsing (HPR) have been employed. This kind of Nb 6 GHz cavity purification allow to reduce hydrogen, oxygen and other elemental impurities content, which effects on cavity Q-factor degradation, by a rapid annealing over 2000°C and a subsequent rapid reduction at room temperature.

Slides TUIOC05 [42.171 MB]

TUIOC06

Study on Optimum Electron Beam Welding Condition for Superconducting Accelerating Cavities

cavity, electron, experiment, SRF

424

T. Kubo, Y. Ajima, H. Inoue, T. Saeki, K. Umemori, Y. Watanabe, S. Yamaguchi, M. Yamanaka
KEK, Ibaraki, Japan
T. Nagata
ULVAC, Inc., Tsukuba, Japan

Optimizations of electron beam welding conditions might solve the quench problems and improve the accelerating field of the superconducting radio-frequency cavity. As a first step toward optimum conditions, basic properties of weld beads are studied by using niobium test pieces. Effects of a combination of a beam generator position and a welding direction on geometries of weld bead are shown. Good parameter-regions for electron beam welding, which yield full penetration welds without holes or weld spatters, are surveyed. Microscopic structures, such as pits or bumps due to poor welds, have greater influence on cavity performances, which are also our research objects. We introduce a model of the magnetic field enhancement at pits, where a formula for a magnetic field enhancement factor is given as a function of parameters that express a geometry of pit. Comparisons between calculations and vertical test results are also shown.

Slides TUIOC06 [15.958 MB]

TUP009

Magnetic Dependence of the Energy Gap: a Good Model to Fit Q Slope of Low Beta Cavities

cavity, superconductivity, experiment, simulation

438

D. Longuevergne
IPN, Orsay, France

The reasons why the intrinsic quality factor (noted Qo) of a superconducting cavity drops with the accelerating field (noted Eacc) are still not well understood. In an effort to explain this phenomenon, mainly for high beta cavities, many models have been developed in the community but few of them could fit experimental data whatever the material treatment or surface conditioning. In the specific case of low beta cavities made of bulk Niobium (i.e Spiral 2 Quarter Wave Resonator), a model based on a magnetic field dependence of the energy gap has been developed to fit experimental data. The evolutions of the model input parameters depending on the cavity treatment or test conditions are consistent with the changes described in the literature. The model will be described and specific examples will be given.

TUP010

Simulation of Non-linear RF Losses Derived from Characteristic Nb Topography

cavity, simulation, SRF, interface

441

C. Xu, M.J. Kelley
JLAB, Newport News, Virginia, USA
M.J. Kelley, C. Xu
The College of William and Mary, Williamsburg, USA
C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A simplified model has been developed to simulate non-linear rf losses on Nb surfaces due exclusively to topographical enhancement of surface magnetic fields. If local sharp edges are small enough, where local surface fields exceed Hc, small volumes of material may become normal conducting without thermal runaway leading to quench. These small volumes of normal material yield increases in the effective surface resistance of the Nb. Using topographic data from typical BCP’d and EP’d fine grain niobium, we have simulated field-dependent losses and find that when extrapolated to resulting cavity performance correspond well to characteristic BCP/EP high field Q0 performance differences for fine grain Nb. We will describe the structure of the model, its limitations, and the effects of this type of non-linear loss contribution to SRF cavities.

TUP011

A Parametric Study of BCS RF Surface Impedance with Magnetic Field Using Xiao Code

impedance, SRF, superconductivity, survey

444

C.E. Reece
JLab, Newport News, Virginia, USA
B. P. Xiao
JLAB, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A recent new analysis of field-dependent BCS RF surface impedance based on moving Cooper pairs has been presented.* Using this analysis coded in Mathematica™, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the “best theoretical” performance available to potential applications with corresponding materials.
* Xiao B. P. et al, Physica C: Superconductivity, 490, 2013, pp. 26–31

TUP014

Fast Table Top Niobium Hydride Investigations Using Direct Imaging in a Cryo-Stage

cavity, cryogenics, laser, vacuum

447

F.L. Barkov, A. Grassellino, A. Romanenko
Fermilab, Batavia, USA

Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
Performance of niobium SRF cavities can be strongly affected by hydrogen segregation into lossy niobium hydrides as known for "hydrogen Q disease" at higher concentration of dissolved H and may be a reason for the "high field Q slope" at lower concentrations. With the use of optical cryostat and laser confocal microscope we have developed a "table top technique" for direct observation of hydride precipitation, and studied formation, morphology, and time evolution of hydrides after different treatments used for cavities. Our results show that hydrides can form at the niobium surface at 90-180K depending mainly on H concentration and the cooldown rate. A lot of H is absorbed by bulk niobium during mechanical polishing, which leads to the formation of very large (>10 microns) hydrides. Both EP and BCP do not influence H concentration significantly provided that temperature during treatments is kept below 15C. 800C degassing reduces H concentration and precludes large hydride precipitation. 120C baking and mechanical deformation do not change H concentration but affect hydride precipitation through their influence on the number of nucleation centers and H binding defects.

TUP015

Bitter Decoration Studies of Magnetic Flux Penetration Into Cavity Cutouts

SRF, experiment, cavity, radio-frequency

451

F.L. Barkov, A. Grassellino, A. Romanenko
Fermilab, Batavia, USA
L.Y. Vinnikov
ISSP, Chernogolovka, Russia

Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Magnetic flux penetration may produce additional losses in superconducting radio frequency cavities. All the existing models for flux penetration are based on the formation of Abrikosov vortices. Using high resolution Bitter decoration technique we have investigated magnetic flux distribution patterns in cavity cutouts at the perpendicular magnetic fields of 10-80 mT. At low fields <20 mT the magnetic field penetrates in the form of flux bundles and not Abrikosov vortices, the situation characteristic of type-I superconductors. With the increase of the magnetic field up to 30 mT "bundles" first merge into a connected structure and then break up into individual Abrikosov vortices at ~60 mT and a well-known intermediate mixed state is observed. Such magnetic field driven transition from type I to type II superconductivity has never been observed before in any existing superconductor. For the case of flat samples we have observed a coexistence of both "bundles" and Abrikosov vortices in one experiment. Our results show that high-purity cavity grade niobium is a "border-line" material and behaves as a type-I superconductor at lower fields and type-II at higher fields.

TUP016

Effects of Processing History on Damage Layer Evolution in Large Grain Nb Cavities

cavity, SRF, electron, radio-frequency

455

D. Kang, T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222.
Previous cavity tests identified a strong dependence of achievable accelerating gradients on the amount of material removed from the surface. Samples extracted from the iris and the equator of a half cell fabricated by Jefferson Lab using large grain Nb were examined to identify underlying mechanisms. Electron backscattered diffraction (EBSD) was used to measure the crystal orientations on the cross sections of the samples. Results demonstrated the presence of a surface damage layer, which contained higher dislocation content than the bulk due to the deep drawing process. The depth of the damage layer depends on crystal orientations, and damage to the iris is more severe than at the equator. From the EBSD data, the damage depth was estimated to be about 100 microns. The samples were then heat treated at 800°C and 1000°C, and the same areas were examined again for the effects of heat treatment on the healing of the damage layer. While the damage layer accounts for some of the performance gain from chemical surface removal, the depth of the damage layer in polycrystalline cavities remains an open question.

TUP017

Study of Slip and Dislocations in High Purity Single Crystal Nb for Accelerator Cavities

cavity, SRF, radio-frequency, factory

461

D. Kang, D.C. Baars, T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222.
SRF Cavities can be formed by deep drawing slices from Nb ingots with large grains. Crystal orientation dependent slip system activities affect the shape change of ingot slices during deep drawing, and form a dislocation substructure that affects subsequent recrystallization and ultimately, cavity performance. Two groups of single crystal tensile specimens with different orientations were extracted from a large grain ingot slice. The first group was deformed monotonically to 40% engineering strain. Analysis revealed that slip was preferred on {112} planes. The second group was heat treated at 800°C for two hours, and then deformed incrementally to 40% engineering strain using an in situ tensile stage. Crystal orientations and surface images were recorded at each increment of deformation. Results indicate that the heat treated group had lower yield strengths, and the details of slip activity differed in the annealed samples. Active slip systems were investigated and compared to the first group. Direct observations of dislocations were performed in selected specimens using electron channeling contrast imaging, to determine how slip affects the dislocation substructure.

TUP022

Study of AC/RF Properties of SRF Ingot Niobium

cavity, SRF, radio-frequency, superconductivity

469

P. Dhakal, G. Ciovati, G.R. Myneni
JLAB, Newport News, Virginia, USA
V.M. Genkin, M.I. Tsindlekht
The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem, Israel

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In an attempt to correlate the SRF performance of niobium cavities with the superconducting properties, we present the results of the magnetization and ac susceptibility of the niobium used in the superconducting radiofrequency cavity fabrications which were subjected to buffer chemical polishing surface and high temperature heat treatments, typically applied to the SRF cavities fabrications. The analysis of the results show the different surface and bulk ac conductivity for the samples subjected to BCP and HT. Furthermore, the RF surface impedance is measured on the sample using the TE011 microwave cavity for a comparison to the low frequency measurements.

TUP023

Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities

SRF, site, superconducting-RF, superconductivity

472

G.V. Eremeev, A.D. Palczewski
JLAB, Newport News, Virginia, USA

Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique[*]. The data differed from measurements done in 80’s that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields and RF resistances at the breakdown site.
[*] G. Eremeev et al.,. In Proceedings of the 15th Superconducting RF conference,pp. 746-749, July 2011.

TUP026

Performance of a FNAL Nitrogen Treated Superconducting Niobium Cavity at Cornell

cavity, SRF, linac, superconductivity

475

D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A. Grassellino
Fermilab, Batavia, USA

Funding: NSF
In many tests of superconducting cavities, the performance of the cavity in the medium field region will be limited by medium field Q slope. For projects such as the proposed Cornell Energy Recovery Linac, high Q operation at medium fields is necessary to meet specifications for efficient CW cavity operation. A single cell cavity was prepared by Fermilab by electropolishing it and baking it at 1000°C with 1x10^-2 Torr of Nitrogen, and subsequently tested at Cornell. The cavity displayed an increase in Q at medium fields between 5 and 20 MV/m at 2.0 K, opposite of the usual medium field Q slope. The material properties of this cavity were studied and correlated with performance. This analysis helps to better understand how to overcome medium field Q slope and improve cavity performance in future CW SRF machines such as the Cornell ERL.

TUP027

High Q0 Studies at Cornell

cavity, SRF, factory, linac

478

D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF
The construction and preparation of superconducting RF cavities with very high quality factors is very advantageous for future particle accelerators operating in CW mode. Until recently, the highest quality factors measured in SRF cavities were on the order of 10¹¹. A Cornell ERL single-center-cell cavity was prepared with BCP and a five day heat treatment at 1000°C. Following this treatment, the cavity was tested and achieved a record high intrinsic quality factor of 2.9·10¹¹ at 1.4 K, corresponding to a very small residual resistance of (0.35±0.10) nOhm. This cavity was then given a series of BCP’s of 5, 75, and 200 μm and retested. Material properties were extracted from the data hinting at a very low mean free path of the niobium. In this paper we discuss the unusual material properties of the surface layer of the cavity and their implication for the RF performance of the cavity.

TUP029

Heat Treatment of SRF Cavities in a Low-Pressure Atmosphere

cavity, vacuum, SRF, resonance

487

D. Gonnella, F. Furuta, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF
Recent results from FNAL on baking superconducting RF cavities at high temperatures in a low-pressure atmosphere of a few mTorr indicate that such treatments can increase the medium field quality factor. In this paper we report on studies from Cornell, giving new insight into the mechanism behind this effect.

TUP033

Magnetic Property Improvement of Niobium Doped with Rare Earth Elements

cavity, experiment, SRF, electron

490

F.S. He, F. He, F. Jiao, X.Y. Lu, K. Zhao
PKU, Beijing, People's Republic of China
L. Chen
NNIEC, Shizuishan City, Ningxia, People's Republic of China
T.C. Jiang
IMP, Lanzhou, People's Republic of China
Y. You, H.Y. Zhao
Ningxia Orient Tantalum Industry Co., Ltd., Dawukou District, Shizuishan city, People's Republic of China

A new idea of modifying the raw niobium was proposed by PKU in 2010, by introducing rare earth elements of Sc and Y into Nb ingot during smelting process. Test results on small samples were very promising*: the Tc was same as Nb, while the Hc1 and Hc2 were increased by 500-700 Oe and up to 4000 Oe, respectively. Recently one Nb ingot doped with Sc was successfully smelted under the collaboration of PKU and OSTEC at Ningxia, and two TESLA-type half cells were fabricated out of the new material by deep drawing. The Hc1 measured from the drop-off of the blanks were consistently high. The RRR was 127, while the mechanical properties met the ILC requirement. One single cell cavity is being fabricated, and vertical test is planned to study the SRF properties of the new material. There is a good chance that the quenching could be pushed to a higher gradient. Another innovative idea of doping only the surface layer of bulk Nb by ion implantation in the pelletron at PKU is also being investigated, in order to improve the SRF performance of the surface layer while maintaining the high thermal conductivity of bulk Nb. Some initial testing results of the new method will be reported as well.
* TTC2012 at JLab:
https://www.jlab.org/indico/getFile.py/access?contribId=78&sessionId=8&resId=0&materialId=slides&confId=24

TUP037

Dynamic Hardening Rule; a Generalization of the Classical Hardening Rule for Crystal Plasticity

experiment, simulation, SRF, controls

499

A. Mapar, F. Pourboghrat
MSU, East Lansing, USA
T.R. Bieler
Michigan State University, East Lansing, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222.
The mechanical properties of a niobium (Nb) specimen can change with the orientation of the sheet. This anisotropy causes inhomogeneity in manufactured SRF cavities. Large grain Nb sheets are more anisotropic and less expensive than fine grain sheets. Designing a manufacturing process for large grain Nb sheets, however, is extremely complex, and requires using advance modeling techniques. A model capable of accurately predicting the deformation behavior of Nb can help improve the performance and reduce costs of a SRF cavity. Optimal design of the manufacturing of cavities with tube hydroforming process is possible with such a model. Crystal plasticity modeling of FCC materials has been very successful; however, there is still no model that can accurately predict the deformation behavior of BCC materials like the large grain Nb sheet. In this study, authors have proposed a dynamic hardening rule for crystal plasticity that significantly improves predictions of the model for large grain Nb. This model is the generalization of the classical hardening rule, and gives better control over the hardening rate. It also increases the stability of the model.

TUP043

Nanostructural TEM/STEM Studies of Hot and Cold Spots in SRF Cavities

cavity, electron, SRF, vacuum

504

Y. Trenikhina, J. Zasadzinski
IIT, Chicago, USA
A. Romanenko
Fermilab, Batavia, USA

Direct TEM/STEM imaging and spectroscopic chemical characterization by EELS/EDS of the surface of the SRF cavity cutouts before and after the treatments (e.g. in situ mild vacuum bake and rinsing with hydrofluoric acid) down to subnanometer scale is implemented to correspond the changes in niobium surface to the SRF performance of the cavities. We also report current results of the direct search, using cryogenic TEM stage, for suggested phase transformations in the niobium-hydrogen system* on “hot” and “cold” spot cavity cutouts, which may help clarifying the mechanism of the high field Q slope and its empirical cure.
*A. Romanenko, F. Barkov, L. D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26 (2013) 035003.

TUP047

Niobium Cavity Electropolishing Modelling and Optimisation

cathode, SRF, simulation, cavity

518

L.M.A. Ferreira, S. Calatroni, S. Forel
CERN, Geneva, Switzerland
J.A. Shirra
Loughborough University, Leicestershre, United Kingdom

It’s widely accepted that electropolishing is the most suitable surface finishing process to achieve high performance bulk Nb accelerating cavities. At CERN, as part of the R&D studies for the 704 MHz high-beta SPL cavities, a new vertical electropolishing facility has been assembled and a study is on-going for the modelling of electropolishing on cavities with COMSOL software. In a first phase, the electrochemical parameters were taken into account for a fixed process temperature and flow rate, and are presented in this poster as well as the results obtained on a real SPL single cell cavity. The procedure to acquire the data used as input for the simulation is presented. The modelling procedure adopted to optimise the cathode geometry, aimed at a uniform current density distribution in the cavity cell for the minimum working potential and total current is explained. Some preliminary results on fluid dynamics and Joule effect are also briefly described.

TUP052

Study on Vertical Electro-Polishing by Cathode With Variable-Geometry Wings

cavity, experiment, cathode, scattering

530

Y.I. Ida, K.N. Nii
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi, Y.B. Iwabuchi
MGI, Chiba, Japan

We have been studying on Vertical Electro-Polishing (VEP) of Nb superconducting accelerator cavity for about one year with a view to the mass-production and cost-reduction of Electro-Polishing (EP) process. Marui Galvanizing Co. Ltd. has been in the EP business of various metals for long time and we have matured experience on EP processes. With being based on the experience, we thought that uniform electric-current on the surface of cavity and effective flow of electrolyte in the cavity are important factors. Moreover, we thought the most important effect is given if the cathode and the cavity surface (anode) are kept in a constant distance. Following these considerations, we invented VEP process by a cathode with variable-geometry wings. Using this cathode, we performed several experiments of VEP Nb single-cell cavities as well as fluid circulation test by plastic 9-cell mock-up. In this article, we will report this unique VEP process, which might be applicable to the mass-production process of International Linear Collider (ILC).

TUP054

Electropolishing of Niobium SRF Cavities in Low Viscosity Aqueous Electrolytes Without Hydrofluoric Acid

cavity, SRF, experiment, controls

540

E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder
Faraday Technology, Inc., Clayton, USA
A.M. Rowe
Fermilab, Batavia, USA

Funding: U.S. DOE Purchase order No. 594128
Electropolishing of niobium materials and cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acid. The use of these dangerous and ecologically damaging chemicals requires careful attention to safety protocol to avoid harmful worker exposure and environmental damage. In this poster we present an approach based on bipolar voltage fields enabling the use of low viscosity water based electrolytes without hydrofluoric acid for electropolishing of niobium materials. The subtleties of the bipolar electropolishing process vis-a-vis conventional electropolishing will be presented.

TUP055

Electropolishing of the ANL Deflecting Cavity for the APS Upgrade

cavity, SRF, background, coupling

544

Y. Yang, J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu
ANL, Argonne, USA
A.C. Crawford
Fermilab, Batavia, USA
P. Dhakal, J.D. Mammosser, H. Wang
JLAB, Newport News, Virginia, USA
Y. Yang
TUB, Beijing, People's Republic of China

Studies on the application of electropolishing (EP) of the ANL superconducting deflecting cavity have shown promising results. This cavity geometry is a squashed single-cell cavity with Y-end group waveguide as well as on-cell LOM damper. The cavity works at TM110-like deflecting mode, in which the iris between the cavity cell and the Y-end group is the highest magnetic field region. Before EP, the cavity had been chemically etched (BCP) several times. Forty-um EP processing was performed on one Mark II prototype deflecting cavity at Fermilab. No mild baking was performed before the cavity vertical test. The test showed that the low-field Q had improved from 2·10⁹ to 3·10⁹ and the high-field Q-slope had been successfully removed. The quench limit was slightly improved from 10⁶ mT to 113 mT. Fast T-mapping had detected a significant decrease of local temperature rise in the cavity iris. Optical inspection before EP found a lot of grooves around the iris, which might be related to the gas bubbles generated during BCP. This suggests that horizontal EP is a promising processing technique to remove the high-field Q-slope and improve the deflecting cavity performance.

TUP057

Plasma Processing R&D for the SNS Superconducting Linac RF Cavities

plasma, cavity, linac, cryomodule

551

M. Doleans, W. Blokland, M.T. Crofford, D.L. Douglas, M.P. Howell, S.-H. Kim, P.V. Tyagi
ORNL, Oak Ridge, Tennessee, USA
R. Afanador, J.A. Ball, B. DeGraff, B.S. Hannah, S.W. Lee, C.J. McMahan, J. Saunders
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE
The Spallation Neutron Source routinely operates with a proton beam power of 1 MW on its production target. A plan to reach the design 1.4 MW within a few years is in place* and relies on increasing the ion beam current, pulse length and beam energy in the linac. The increase in beam energy from the present 930 MeV to 1 GeV will require an increase of approximately 15% in the accelerating gradient of the superconducting linac high-beta cryomodules. In-situ plasma processing was identified as a promising technique** to reduce electron activity in the SNS superconducting cavities and increase their accelerating gradient. R&D on plasma processing aims at deploying the new in-situ technique in the linac tunnel by 2016. Overall plan and current status of the plasma processing R&D will be presented.
* NScD Five year plan 2012-2016, SNS-NSCD-EXE-PN-0001, R00, ORNL
** S-H Kim et al., “R&D Status for In-Situ Plasma Surface Cleaning of SRF Cavities at Spallation Neutron Source”, PAC 2011 Proceedings

TUP058

Recent Findings on Nitrogen Treated Niobium

cavity, SRF, vacuum, solenoid

558

R.G. Eichhorn, A. Ganshin, A. Holmes, J.J. Kaufman, S.R. Markham, S. Posen, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Recent findings on Nitrogen treated Niobiums Based on recent findings at Fermilab, Cornell investigated the role of Nitrogen being present during the cavity hydrogen degassing process. We treated several samples at different temperatures being exposed to nitrogen between 10 minutes and 3 hours at pressures around 15 mbar as well as single cell cavities. This contribution will summarize our findings from surface analysis, Tc measurements and cavity Qs, addressing the question, if such a process can form Niobium-Nitride.

TUP060

Acid Free Extended Mechanical Polishing R&D

cavity, SRF, electron, radio-frequency

564

C.A. Cooper, A.C. Crawford, C.M. Ginsburg, A. Grassellino, R.D. Kephart, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov
Fermilab, Batavia, USA

We report the progress in the development of a centrifugal barrel polishing recipe which can lead to standard cavity performance without the need of any chemical treatments. Q ~ 10¹⁰ at 20 MV/m and gradients above 35 MV/m have already been demonstrated for cavities whose preparation sequence was CBP, degassing and no subsequent chemical treatments. Results of studies on the effect of different CBP media on RF performance will be reported, including full body T-map showing the distribution of RF losses.

TUP062

Application of In-Vacuum Infrared Pyrometry During Fabrication of European XFEL Niobium Cavities

cavity, vacuum, operation, electron

570

L. Monaco, P. Michelato, D. Sertore
INFN/LASA, Segrate (MI), Italy
V. Battista, G. Corniani, M. Festa
Ettore Zanon S.p.A., Schio, Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

A technique to measure the temperature of Niobium components in vacuum during Electron Beam Welding (EBW) operation is presented and results obtained on the large scale cavity production for the European XFEL are discussed. During the EBW process, the knowledge of the components temperature during the welding operation could help both for the better choice of the welding parameters and for the optimization of the production cycle. In collaboration with the Italian firm Ettore Zanon (EZ), we developed a system able to measure the temperature of Nb components in vacuum during EBW operation using a IR pyrometer placed outside the vacuum chamber through an appropriate vacuum viewport. In the paper the experience of this device during the production of Nb components for the XFEL 1.3 GHz cavity production is discussed.

TUP063

Quench Studies and Preheating Analysis of Seamless Hydroformed Cavities Processed at Jefferson Laboratories

cavity, SRF, electron, site

575

A.D. Palczewski, G.V. Eremeev, R.L. Geng
JLAB, Newport News, Virginia, USA
I. Jelezov
RAS/INR, Moscow, Russia
W. Singer, X. Singer
DESY, Hamburg, Germany

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
One of the alternative manufacturing technologies for SRF cavities is hydroforming from seamless tubes. Although this technology has produced cavities with gradient and Q-values comparable to standard EBW/EP cavities, a few questions remain. One of these questions is whether the quench mechanism in hydroformed cavities is the same as in standard electron beam welded cavities. Towards this effort Jefferson Lab performed quench studies on 4 different seamless hydroformed cavities. These cavities include DESY’s – Z163 and Z164 nine-cell cavities, and Black Laboratories nine-cell and two-cell TESLA shaped cavities, hydroformed at DESY. Initial results from the cavities and quench localization were published in SRF2011*. In this report we will present post JLAB surface retreatment quench studies for each cavity. The data will include OST and T-mapping quench localization as well as quench location preheating analysis comparing them to the observations in standard electron beam welded cavities.
*W. Singer, A. Ermakov, G. Kreps, A. Matheisen, X. Singer, K. Twarowski, I. Zhelezov, P. Kneisel, R. Crooks, Proceedings of SRF2011, TUPO026 2011.

TUP064

Exploration of Material Removal Rate of SRF Elliptical Cavities as a Function of Media Type and Cavity Shape on Niobium and Copper Using Centrifugal Barrel Polishing (CBP)

cavity, SRF, superconductivity, status

579

A.D. Palczewski, G. Ciovati, R.L. Geng, Y.M. Li
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Centrifugal barrel polishing (CBP) for SRF application is becoming more wide spread as the technique for cavity surface preparation. CBP is now being used in some form at SRF laboratories around the world. Before the process can become as mature as wet chemistry like eletro-polishing (EP) and buffered chemical polishing (BCP) there are many questions which remain unanswered. One of these topics includes the uniformity of removal as a function of cavity shape and material type. In this presentation we show CBP removal rates for various media types on 1.3 GHz TESLA and 1.5 GHz CEBAF large grain niobium cavities, 1.3 GHz TESLA fine grain niobium cavity, and 1.3GHz low surface field copper cavity. The data will also include calculated RF frequency shift modeling non-uniform removal as a function of cavity position and comparing them with CBP results.

TUP065

Chemical Structure of Niobium Samples Vacuum Treated in Nitrogen in Parallel With Very High Q0 Cavities

cavity, SRF, lattice, accelerating-gradient

583

Y. Trenikhina
IIT, Chicago, USA
A. Grassellino, A. Romanenko
Fermilab, Batavia, USA

XPS in combination with subsequent material removal via Ar sputtering as well as XRD are used for the surface analysis and bulk phase characterization of nitrogen treated samples processed parallel with SRF cavities. We investigated the surface chemistry of the samples treated with nitrogen in order to understand this treatment effect on SRF cavity performance for several baking temperatures and durations in order to find cost efficient post-furnace chemistry free procedures to enable high Q-values.

TUP066

Plasma Processing of Large Surfaces with Application to SRF Cavity Modification

plasma, cavity, SRF, experiment

586

J. Upadhyay, S. Popović, L. Vušković
ODU, Norfolk, Virginia, USA
D.S. Im
Old Dominion University, Norfolk, Virginia, USA
H.L. Phillips, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA

Funding: Supported by DOE under grant no. DE-SC0007879. JU acknowledges support by JSA/DOE via DE-AC05-06OR23177
Plasma based surface modifications of SRF cavities present promising alternatives to the wet etching technology currently applied. To understand and characterize the plasma properties and chemical kinetics of plasma etching processes inside a single cell cavity, we have built a specially-designed cylindrical cavity with 8 observation ports. These ports can be used for holding niobium samples and diagnostic purposes simultaneously. Two frequencies (13.56 MHz and 2.45 GHz) of power source are used for different pressure, power and gas compositions. The plasma parameters were evaluated by a Langmuir probe and by an optical emission spectroscopy technique based on the relative intensity of two Ar 5p-4s lines at 419.8 and 420.07 nm. Argon 5p-4s transition is chosen to determine electron temperature in order to optimize parameters for plasma processing. Chemical kinetics of the process was observed using real-time mass spectroscopy. The effect of these parameters on niobium surface would be measured, presented at this conference, and used as guidelines for optimal design of SRF etching process.

TUP067

Hydrogen Saturation and the Thermal Conductivity of Superconducting Niobium

cavity, superconductivity, vacuum, lattice

589

S.K. Chandrasekaran
MSU, East Lansing, USA
T.R. Bieler
Michigan State University, East Lansing, USA
C. Compton
FRIB, East Lansing, USA
N.T. Wright
(MSU), East Lansing, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-S0004222
The thermal conductivity k of Nb at less than 3 K is dominated by phonon transport. In Nb with sufficiently few lattice imperfections, a maximum in k occurs at 1.8 K, called the phonon peak (PP). A large PP is desired to reduce potential local hot spots and contributes to an increased Q factor. The magnitude of the PP is sensitive to SRF cavity manufacturing processes. The effect of interstitial hydrogen on the magnitude of the PP is examined by subjecting two bicrystal Nb specimens to 300 C for 1 h in a 75% H2, 25% N2 atmosphere at 0.5 atm. Prior to hydrogen infusion, specimen 1 was heated to 800 C for 2 h, while specimen 2 was heated to 1100 C for 4 h. Both specimens displayed a 25% reduction in the PP due to the additional hydrogen, independent of their crystal orientations and heat treatment histories. An 800 C vacuum heating for 2 h was found to be sufficient to recover the PP in specimen 1, while an 1100 C heating for 4 h was required to recover the PP in one of the grains of specimen 2. The results suggest that hydrogen trapped in the Nb lattice will degas when the Nb is heated to at least the temperature to which it was heated at prior to the hydrogen infusion step.

TUP068

Laser Polishing of Niobium for SRF Applications

laser, experiment, SRF, simulation

593

L. Zhao, M.J. Kelley
The College of William and Mary, Williamsburg, USA
M.J. Kelley, J.M. Klopf, C.E. Reece
JLAB, Newport News, Virginia, USA
L. Zhao
JLab, Newport News, Virginia, USA

Smooth interior surfaces are desired for niobium SRF cavities, now obtained by buffered chemical polish (BCP) and/or electropolish (EP). Laser polishing is a potential alternative, having advantages of speed, freedom from chemistry and in-process inspection. Here we show that laser polishing can produce smooth topography with Power Spectral Density (PSD) measurements similar to that obtained by EP. We studied the influence of the laser power density and laser beam raster rate on the surface topography. These two factors need to be combined carefully to smooth the surface without damaging it. Computational modeling was used to simulate the surface temperature and explain the mechanism of laser polishing.

Poster TUP068 [1.011 MB]

TUP070

Characterization of Superconducting Samples With SIC System for Thin Film Developments: Status and Recent Results.

cavity, ECR, SRF, network

599

G.V. Eremeev, H.L. Phillips, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA
C.E. Reece
JLab, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Within any thin film development program directed towards SRF accelerating structures, there is a need for an RF characterization device that can provide information about RF properties of small samples. The current installation of the RF characterization device at Jefferson Lab is Surface Impedance Characterization (SIC) system. The data acquisition environment for the system has recently been improved to allow for automated quicker measurement, and the system has been routinely used for characterization of bulk Nb, films of Nb on Cu, MgB2, NbTiN, Nb3Sn films, etc. We present some of the recent results that illustrate present capabilities and limitations of the system.

TUP071

Development of Nb3Sn Cavity Vapor Diffusion Deposition System

cavity, vacuum, impedance, controls

603

G.V. Eremeev, W.A. Clemens, K. Macha, H. Park, R.S. Williams
JLAB, Newport News, Virginia, USA
H. Park
ODU, Norfolk, Virginia, USA

Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Alternative BCS superconductors with the superconducting critical temperature higher than that of niobium theoretically surpass the limitations of niobium. The feasibility of technology has been demonstrated at 1.5 GHz with Nb3Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb3Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb3Sn vapor diffusion deposition system within an R&D development program towards compact light sources. Here we present the current progress of the system development.

TUP072

Quality Factor Measurements of the Ultramet 3 GHz Cavity Constructed Using Chemical Vapour Deposition

cavity, SRF, radio-frequency, operation

607

D.L. Hall, D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V.M. Arrieta, S.R. McNeal
Ultramet, California, USA

Funding: US Department of Energy Phase 1 Small Business Innovation Research award to Ultramet
A seamless 3 GHz bulk niobium cavity constructed by Ultramet using rapid chemical vapor deposition (CVD) techniques has been tested on the vertical SRF test stand at Cornell. The cavity received a 25 um buffered chemical polish (BCP) and 700 C heat treatment for 4 days. First test results gave an intrinsic quality factor of Q0 = (1.55 ± 0.12) x 10⁷ and (2.00 ± 0.15) x 10⁷ at 4.2 K and 1.5 K, respectively. A second BCP removed 100 um of material, after which test results improved to Q0 = (7.59 ± 1.52) x 10⁷ and (4.16 ± 0.31) x 10⁸ at 4.2 K and 1.5 K. During the ﬁrst test poor coupling to the input ampliﬁer impeded tests at accelerating ﬁelds >0.2 MV/m, while during the second test the cavity quenched at 1.3 MV/m when operating at 1.5 K. An optical inspection of the cavity after the second test revealed the presence of at least 4 pits on the upper hemisphere suggesting an area of higher than average surface resistance that may have contributed to the low ﬁeld quench via thermal runaway. The potential of CVD as a construction method for SRF cavities is discussed.

TUP073

Niobium Coatings for the HIE-ISOLDE QWR Superconducting Accelerating Cavities

cavity, vacuum, cathode, SRF

611

N.M. Jecklin, S. Calatroni, L.M.A. Ferreira, I. Mondino, A. Sublet, M. Therasse, W. Venturini Delsolaro
CERN, Geneva, Switzerland
B. Delaup
EPFL, Lausanne, Switzerland

The HIE-ISOLDE project is the upgrade of the existing ISOLDE facility at CERN, which is dedicated to the production of a large variety of radioactive ion beams for nuclear physics experiments. A new linac made of 20 β=10.3% and 12 β=6.3% QWR superconducting accelerating cavities at 101 MHz will be built, and in a first phase two cryomodules of 5 high-beta cavities each are scheduled to accelerate first beams in 2015. The cavities are made of a copper substrate, with a sputter-coated superconductive niobium layer, operated at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses (Q0=4.5e8) In this paper we will discuss the baseline surface treatment and coating procedure which allows obtaining the required performance, as well as the steps undertaken in order to prepare series production of the required number of cavities guaranteeing their quality and functionality.

TUP074

Development of an Optimized Quadrupole Resonator at HZB

quadrupole, cavity, resonance, focusing

614

R. Kleindienst, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

Funding: EuCARD II
Current superconducting cavities are generally made of solid niobium. A possibility to reduce cost as well as increase accelerating fields and, essential for CW applications, the quality factor is to use thin-film coated cavities. Measuring and understanding the RF-properties of superconducting thin films, specifically the surface resistance at the operating field and frequency, is needed to drive forward this development. Presently, only few facilities exist capable of measuring the surface resistance of thin films samples with a resolution in the nano-ohm range at L-Band. We describe here a dedicated test stand consisting of a quadrupole resonator that was constructed at the Helmholtz Zentrum Berlin. Starting with 400-MHz quadrupole resonator developed at CERN, the design was adapted and optimized for resolution and reduced peak electric field to 433 MHz (making available the higher harmonic mode at 1,3GHz) using simulation data obtained with CST Microwave Studio as well as ANSYS. The relevant figures of merit have been improved, giving the possibility to perform measurements with high resolution at high field levels.

TUP075

Design and Commissioning Status of New Cylindrical HiPIMS Nb Coating System for SRF Cavities

cavity, ion, cathode, SRF

617

H.L. Phillips, K. Macha, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA

Funding: † Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
For the past 19 years Jefferson Lab has sustained a program studying niobium films deposited on small samples in order to develop an understanding of the correlation between deposition parameters, film micro-structure, and RF performance. A new cavity deposition system employing a cylindrical cathode using the HiPIMS technique has been developed to apply this work to cylindrical cavities. The status of this system will be presented.

TUP076

Preliminary Results of Nb Thin Film Coating for HIE-ISOLDE SRF Cavities Obtained by Magnetron Sputtering

cavity, plasma, cathode, monitoring

620

A. Sublet, I. Aviles Santillana, S. Calatroni, A. D'Elia, N.M. Jecklin, I. Mondino, S. Prunet, M. Therasse, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland

Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI.
In the context of the HIE-ISOLDE upgrade at CERN, several new facilities for the niobium sputter coating of QWR-type superconducting RF accelerating cavities have been developed, built, and successfully operated. In order to further optimize the production process of these cavities the magnetron sputtering technique has been further investigated and continued as an alternative to the already successfully operational DC bias diode sputtering method. The purpose of this poster is to present the results obtained with this technique. The Nb thickness profile along the cavity and its correlation with the electro-magnetic field distribution inside the cavity are discussed. Film structure, morphology and Residual Resistivity Ratio (RRR) will be considered as well and compared with films obtained by DC bias diode sputtering. Finally these results will be compared with RF characterization and measurement of a production-like magnetron-coated cavity.

TUP077

Thin Film Coating Optimization for HIE-ISOLDE SRF Cavities: Coating Parameters Study and Film Characterization

cavity, cathode, hardware, SRF

623

A. Sublet, I. Aviles Santillana, S. Calatroni, P. Costa Pinto, N.M. Jecklin, S. Prunet, A. Sapountzis, W. Venturini Delsolaro, W. Vollenberg
CERN, Geneva, Switzerland

Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI.
The HIE-ISOLDE project at CERN requires the production of 32 cavities in order to increase the energy of the beam. The Quarter Wave Resonators (QWRs) cavities of complex cylindrical geometry (0.3m diameter and 0.8m height) are made of copper and are coated with a thin superconducting layer of niobium. In the present phase of the project the aim is to obtain a niobium film, using the DC bias diode sputtering technique, providing adequate high quality factor of the cavities and to ensure reproducibility for the future series production. After an overview of the explored coating parameters (hardware and process), the resulting film characteristics, thickness profile along the cavity, structure and morphology (SEM measurements) and Residual Resistivity Ratio (RRR) of the Nb film will be shown. The effect of the sputtering gas process pressure and configuration of the coating setup will be highlighted.

TUP078

Nb Coating Developments with HIPIMS for SRF Applications

cavity, target, plasma, cathode

627

G. Terenziani, I. Aviles Santillana, S. Calatroni, T. Junginger
CERN, Geneva, Switzerland
A.P. Ehiasarian
SHU, Sheffield, United Kingdom

In the last few years the interest of the thin film science and technology community on High Impulse Power Magnetron Sputtering (HIPIMS) coatings has steadily increased. HIPIMS literature shows that better thin film morphology, denser and smoother films can be achieved when compared with standard dc Magnetron Sputtering (dcMS) coating technology. Furthermore the capability of HIPIMS to produce a high quantity of ionized species can allow conformal coatings also for complex geometries. A study is under way at CERN to apply this technology for the Nb coating of SRF 1.3-1.5 GHz Cu cavities, and in parallel at SHU the plasma physics and its correlation with film morphology are being investigated. Recent results achieved with this technique are presented in the paper.

TUP081

Chemical Vapor Deposition Techniques for the Multilayer Coating of Superconducting RF Cavities

cavity, SRF, controls, experiment

635

F. Weiss, C. Jimenez, S. Pignard
Institut Polytechnique de Grenoble, Grenoble INP, Grenoble, France
C.Z. Antoine
CEA/IRFU, Gif-sur-Yvette, France
M. Benz, E. Blanquet, R. Boichot, A. Mantoux, F. Mercier
Laboratoire SIMAP, Grenoble-INP, CNRS, UJF, Saint Martin d'Hères, France

Issued from the recent development of thin films technologies, multilayer nanostructures face today very challenging questions in materials science: ultimate size reduction, process control at an atomic scale, new size driven properties and system characterisation. For superconducting RF technologies a significant breakthrough could arise from the use of multilayered structures deposited inside Nb cavities. These multilayer nanostructures are based on the use of some 10 nanometers thick superconducting layers (d<λL) with a higher Tc than in Nb, alternating with insulating layers, required to decouple the superconducting films. We present here our first studies devoted to nano-layered superconductors produced by Chemical Deposition techniques: CVD and ALD. The basic principles of CVD and ALD will be presented together with new developments of the coordination chemistry for the ALD precursors, which is key point for the optimization of the individual layers. First results concerning NbN films obtained by CVD as well as CVD and ALD results concerning insulating materials used for Superconducting/insulating (S/I/S/I) multilayers structures will be reported.

TUP083

Film Deposition, Cryogenic RF Testing and Materials Analysis of a Nb/Cu Single Cell SRF Cavity

cavity, cryogenics, SRF, plasma

642

X. Zhao
JLab, Newport News, Virginia, USA
R.L. Geng, Y.M. Li, A.D. Palczewski
JLAB, Newport News, Virginia, USA
Y.M. Li
PKU, Beijing, People's Republic of China

Funding: The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DEAC05- 06OR23177.
In this study, we present preliminary results on using a cathodic-arc-discharge Nb plasma ion source to establish a Nb film-coated single-cell Cu cavity for SRF research. The polycrystalline Cu cavity was fabricated and mirror-surface-finished by a centrifugal barrel polishing (CBP) process at Jefferson Lab. Special pre-coating processes were conducted, in order to create a template-layer for follow-on Nb grain thickening. A sequence of cryogenic RF testing demonstrated that the Nb film does show superconductivity. But the quality factor of this Nb/Cu cavity is low as a result of high residual surface resistance. We are conducting a thorough materials characterization to explore if some microstructural defects or hydrogen impurities, led to such a low quality factor.

TUP085

Study of NbTi Welded Parts

cavity, laser, plasma, linac

659

N. Bazin, C.Z. Antoine
CEA/DSM/IRFU, France
C. B. Baumier, G. Martinet
IPN, Orsay, France
F. F. Fortuna
CSNSM, ORSAY CAMPUS, France
J.-B. Sirven
Commisariat à l'Energie Atomique (CEA/DEN/DPC), Direction de l'Energie Nucléaire, Gif-sur-Yvette, France

Due to its properties, niobium-titanium alloy is widely used to manufacture the flanges of superconducting niobium accelerating cavities. The material hardness is compliant to provide UHV-tight connections with aluminum gaskets or spring-type gaskets (Helicoflex). And the alloy can be directly welded to the niobium. The paper will present the surface analysis made on NbTi samples after the chemical treatment and on a Nb / NbTi weld.

TUP086

Cryogen-Free RF System Studies Using Cryocooler-Cooled Magnesium Diboride-Coated Copper RF Cavities

cavity, cryomodule, SRF, accelerating-gradient

663

A. Nassiri, R. Kustom, Th. Proslier
ANL, Argonne, USA
T. Tan, X. Xi
TU, Philadelphia, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357.
Studies on the application of magnesium diboride(MgB2)high-Tc superconducting films have shown promise for use with rf cavities. Studies are directed towards applying the films to niobium cavities with the goal to increase accelerating gradients to greater than 50 MeV/m. However, studies also have shown that MgB2 films, with a critical temperature over four times higher than Nb, have surface resistances equal, or nearly equal, at 8-12 K, to what is achieved with niobium at 4 K. It might be possible to design and operate cavity systems in the 8-12K temperature range with cryocoolers that are currently available. The current cryocoolers can remove as much as 20 watts per unit in the range of 8-12K. This suggests that helium-free superconducting RF systems are possible for future light sources and possible industrial and medical linear accelerators. Our current research is directed towards depositing MgB2 films onto copper, or other high thermal conductivity metal, substrates which would allow future cavities to be fabricated as film coated copper structures. We have started atomic layer deposition and Hybrid chemical vapor deposition studies of MgB2 on 2-inch copper coupons.

TUP087

RF Test Results of the first Nb3Sn Cavities Coated at Cornell

cavity, SRF, operation, linac

666

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

As an alternative material to niobium for SRF cavities in particle accelerators, Nb3Sn presents two significant advantages. With a Tc of 18 K, it has a very small surface resistance at a given temperature, leading to a significant reduction in cryogenic costs; and with a predicted Hsh of nearly 400 mT, it has the potential to produce cavities with higher gradients and therefore shorter high energy linacs. Recently, two 1.3 GHz cavities have been fabricated and coated with Nb3Sn at Cornell. Tests of these first cavities have produced encouraging results, including a very high Tc and some very high-performing surface regions. These cavity results as well as new results of samples studied using TEM will be presented.

TUP097

Study of the Temperature Interface Between Niobium and Superfluid Helium. Temperature Waves Measurements from Heat Sources

cavity, SRF, factory, radio-frequency

700

A. Ganshin, F. Furuta, D.L. Hartill, G.H. Hoffstaetter, K.M. Price, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431.
One of the most important properties of Superconducting Radio Frequency (SRF) cavities is their ability to disperse generated heat from the internal cavity wall to the external super fluid helium bath. When the generated heat is not removed fast enough, an effect known as thermal feedback dominates, resulting in medium field Q-slope. This medium field Q-slope has the ability to reduce the Q factor should it become strong enough. To determine what physical factors affect the creation of the medium field Q-slope we will be computationally modeling the medium field Q-slope with varying parameters, such as Kapitza conductivity, wall thickness, RF frequency, bath temperature, residual resistivity ratio, residual resistance, and phonon mean path. Our results show that the medium-field Q slope is highly dependent on the Kapitza conductivity and that by doubling the Kapitza conductivity the medium field Q-slope reduces significantly. Understanding and controlling the medium ﬁeld Q-slope will benefit future continuous wave (CW) applications such as the Energy Recovery Linacs (ERL) where cryogenics costs dominate due to CW operation at medium ﬁelds (< 20 MV/m).

TUP100

Medium Field Q-Slope Studies in High Frequency Cavities

cavity, operation, superconductivity, factory

705

O.S. Melnychuk, A. Grassellino, A.I. Sukhanov
Fermilab, Batavia, USA

A phenomenon of Medium Field Q-Slope (MFQS) in superconducting RF cavities is of high importance because it occurs in the field range (5-20MV/m) that includes designed operation fields of future CW accelerators. MFQS impacts resistive losses in the cavity and, consequently, directly affects accelerator operation costs. We present studies of MFQS based on vertical test data for 1.3GHz nine-cell cavities and make comparisons of vertical test data from different laboratories.

TUP108

Study on Niobium Scratch and Tantalum or Carbonaceous Contamination at Niobium Surface with Field Emission Scanner

cavity, electron, site, controls

731

S. Kato, H. Hayano, T. Kubo, T. Noguchi, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan

It is mandatory to investigate field emission from niobium SRF cavity surface systematically since even small field emission often limits the cavity performance terribly. The field emission strength and the number of emission sites strongly depend on niobium surface properties which are determined by its surface treatment and handling. It was found that carbonaceous contamination including carbon, oxygen, sometimes, nitrogen often segregates at CPed or EPed surface with a size of several micron to several tens of micron-meters. There is a strong doubt that this contamination causes field emission from the surface. Newly developed field emission scanner (FES) allows us to measure a distribution of the field emitting sites over a sample surface at a given field strength along with its SEM (scanning electron microscope) observation and EDX (energy dispersive x-ray) analysis. This article describes results of the FES-SEM-EDX application to carbonaceous contamination at niobium surface.

TUP110

An X-Ray Fluorescence Probe for Defect Detection in Superconducting 1.3 GHz Cavities

cavity, detector, embedded, radiation

736

P. Michelato, M. Bertucci
INFN/LASA, Segrate (MI), Italy
A. Navitski, W. Singer, X. Singer
DESY, Hamburg, Germany
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
Y. Tamashevich
Uni HH, Hamburg, Germany

The aim of this project is to develop a system for defect detection by means of X-ray fluorescence (XRF) analysis. XRF is a high sensitivity spectroscopy technique allowing the detection of trace element content, such as the few microgram impurities, responsible for low cavity performances if embedded in the equatorial region during cavity manufacturing. The proposed setup is customized on 1.3 GHz TESLA-type niobium cavities: both the detector and the X-ray excitation source are miniaturized so to allow the probe to enter within the 70 mm iris diameter and aside of the HOM couplers. The detection-excitation geometry is focused on cavity cell equator surface located at about 10³ mm from the cavity axis, with an intrinsic spot-size of about 10 mm. The measuring head will be settled on a high angular resolution optical inspection system at DESY, exploiting the experience of OBACHT. Defect position is obtained by means of angular inner cavity surface scanning. A quantitative determination of defect content can also be carried out by means of fundamental parameters technique with a Niobium standard calibration.

TUP111

Experimental Investigations of the Quench Phenomena for the Quench Localization by the Second Sound Wave Method

cavity, SRF, controls, experiment

739

J. Plouin, J.-P. Charrier, C. Magne, J. Novo
CEA/DSM/IRFU, France
L. Maurice
CEA/IRFU, Gif-sur-Yvette, France

The quench localization by the second sound method is now widely used in many laboratories. This method avoids the complicated implementation of temperature arrays around the surface cavities. Instead, specific sensors are placed around the cavity and the time of arrival of the second sound wave generated by the quench is measured on each sensor; then the distance from sensors to quench is deducted from the theoretical second sound wave velocity. In principle, the quench position can be localized with a triangulation by a limited number of sensors. However, many measurements have shown that the time of arrival of the wave was not corresponding to the theoretical second sound wave velocity: the “measured” velocity is often 50% higher than the theory. At CEA-Saclay we performed several measurements on single cell cavities to investigate these phenomena. Several hypotheses are studied: large quench spot, heat propagation by another phenomenon than the second sound near to the cavity where the heat power density is very high. These results and the discussions on these hypotheses will be presented.

TUP112

Time-Resolved Measurements of High-Field Quench in SRF Cavities

cavity, SRF, simulation, accelerating-gradient

743

S. Antipov
University of Chicago, Chicago, Illinois, USA
E. Efimenko
MIPT, Dolgoprudniy, Moscow Region, Russia
A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, USA

Fermilab’s temperature mapping system for SRF cavities has been improved to observe quench dynamics with 1ms time resolution. The increase in sampling rate was achieved by localizing the quench and then performing the measurements using a limited subset of thermometers. Implemented experimental procedure allowed to measure temperature distribution within quench spot, as well as the amount of stored energy, at the moment quench starts, during its growth, and decay. For three tested SRF cavities, quenching at fields 21.7 – 33 MeV/m, maximal radius of the normal zone was 40 – 65 mm; time to return to superconducting state: 90 – 250 ms. In the beginning of the process temperature increase rate in the center of the normal zone is as high as 2.5 K/ms, radius increase rate – 20 mm/ms. The described experimental procedure can be useful for investigating how different surface treatments affect the breakdown, understanding of the nature of high-field quench, improvement of quench detection techniques, and material science research for future SRF cavities.

WEIOA03

Nb Sputtered Quarter Wave Resonators for the HIE-ISOLDE

cavity, cathode, vacuum, linac

767

W. Venturini Delsolaro, S. Calatroni, A. D'Elia, B. Delaup, N.M. Jecklin, Y. Kadi, P. Maesen, I. Mondino, A. Sublet, M. Therasse
CERN, Geneva, Switzerland
A. D'Elia
UMAN, Manchester, United Kingdom
D.A. Franco Lespinasse, G. Keppel, V. Palmieri, S. Stark
INFN/LNL, Legnaro (PD), Italy

The HIE-ISOLDE superconducting linac will be based on quarter wave resonators (QWRs), made by Niobium sputtering on Copper. The operating frequency at 4.5 K is 101.28 MHz and the required performance for the high beta cavity is 6 MV/m accelerating field for 10 W maximum power dissipation. These challenging specifications were recently met at CERN at the end of a vigorous development program. The paper reports on the progress of the cavity RF performance with the evolution of the sputtering process; it equally illustrates the parallel R&D which is ongoing at CERN and at INFN in the quest for even higher performances.

Slides WEIOA03 [14.564 MB]

WEIOA04

Nb3Sn for SRF Application

cavity, SRF, laser, vacuum

773

M. Liepe, S. Posen
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The superconductor Nb3Sn is a promising alternative to standard niobium for SRF applications for two reasons: Its larger superconducting energy gap results in significantly lower BCS surface resistance at typical SRF operating temperatures. Additionally, theoretical predictions suggest that the maximum operating field of Nb3Sn cavities could be twice that of niobium cavities. Early work on a small number of Nb3Sn coated cavities indeed showed 2K to 4.2K quality factors well above what is achievable with niobium, though at accelerating fields below ~10 MV/m only. After many years of worldwide inactivity, Cornell has taken the lead and initiated a new R&D program on Nb3Sn to explore its full potential for SRF applications. New facilities for coating cavities with Nb3Sn have been set up at Cornell, and 1.3 GHz single cell cavities have been coated and tested. This talk presents the Cornell Nb3Sn program, discusses first promising results obtained, and also gives an overview of other Nb3Sn SRF work worldwide.

Slides WEIOA04 [3.854 MB]

WEIOC01

High Resolution Surface Resistance Studies

quadrupole, cavity, shielding, superconductivity

785

S. Aull, S. Döbert, T. Junginger
CERN, Geneva, Switzerland
S. Aull, J. Knobloch
University of Siegen, Siegen, Germany
J. Knobloch
HZB, Berlin, Germany

Funding: Work supported by the German Doctoral Students program of the Federal Ministry of Education and Research (BMBF).
The attempt to reach quality factors beyond 10¹¹ and pushing the accelerating gradients of SRF cavities to the theoretical limit, the treatment depending loss mechanisms in niobium need better understanding. CERNs Quadrupole Resonator enables sub-nΩ-resolution measurements of the surface resistance. The available parameters cover resonant modes at 400, 800 and 1200 MHz, any temperature up to 15 K and rf fields up to 60 mT. Recently the setup has been extended with a coil creating a dc magnetic field for trapped flux studies. Overall, much more information about the rf performance is accessible compared to regular cavity measurements. Since the samples are flat disks of 75 mm diameter geometric fabrication issues are simplified which makes the Quadrupole Resonator also the perfect tool to study alternative materials or new coating techniques. In this contribution in depth studies of a heat treated bulk niobium sample exploiting the complete parameter range of the setup are presented.

Slides WEIOC01 [2.724 MB]

WEIOC02

Multilayers Activities at Saclay / Orsay

cavity, SRF, vacuum, superconductivity

789

C. B. Baumier, G. Martinet
IPN, Orsay, France
C.Z. Antoine
CEA/IRFU, Gif-sur-Yvette, France
F. F. Fortuna
CSNSM, ORSAY CAMPUS, France
J.C. Villegier
CEA/INAC, Grenoble Cedex 9, France

In the investigations on the high gradient SRF cavities, the superconducting multilayer is a promising alternative. The predictions show that an SIS (Superconductor/Isolator/Superconductor) nano-composite could improve the efficiency limited by the bulk Nb it-self used today for accelerating cavities. We start, at the IPNO lab in collaboration with the CSNSM lab (CNRS) and Irfu lab (CEA), an experimental study to test the screening effect on multilayer assemblies. Based on 3rd harmonic magnetometer and a TE011 SRF cavity, measurements of first critical magnetic field HC1 and surface resistance of samples have been performed. Along with these first results, we are starting the development of a MBE deposition. This set-up is devoted to optimise the best organisation of the multilayer to produce the model sample, and to find, in a close future, a realistic solution to apply this technique on an accelerating SRF cavity.
Labex P2IO funding

Slides WEIOC02 [3.035 MB]

WEIOC04

Theoretical Field Limits for Multi-Layer Superconductors

SRF, cavity, experiment, superconductivity

794

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
G. Catelani
Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany
J.P. Sethna
Cornell University, Ithaca, New York, USA
M.K. Transtrum
M.D.A.C.C., Houston, Texas, USA

With modern cavity preparation techniques, niobium SRF cavities reach surface magnetic fields very close to the fundamental limit of the superheating field of the material, and researchers are looking to alternative superconductors to sustain even higher fields. However, these materials may have an increased vulnerability to flux penetration at defects, even small ones, as a result of their short coherence lengths. A. Gurevich has proposed [1] a method of mitigating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the SRF community, to help researchers to optimize cavities made from alternative superconductors.
[1] A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)

Slides WEIOC04 [4.116 MB]

THIOA03

Cavity Fabrication Study in CFF at KEK

cavity, electron, HOM, gun

821

M. Yamanaka, Y. Ajima, H. Inoue, T. Kubo, T. Saeki, Y. Watanabe, S. Yamaguchi
KEK, Ibaraki, Japan

The construction of new facility for the fabrication of superconducting RF cavity at KEK was completed in 2011. It is equipped with the following machines; an electron-beam welding (EBW) machine, a servo press machine and a CNC vertical lathe. A chemical etching apparatus is also equipped. The study on the fabrication of 9-cell cavity for International Linear Collier (ILC) has been started from 2009 using this facility. The study is focusing on the cost reduction with keeping high performance of cavity, and the goal is the establishment of mass-production procedure for ILC.

Slides THIOA03 [7.823 MB]

THIOC01

Low Beta Cavity Development for an ATLAS Intensity Upgrade

cavity, cryomodule, linac, ion

850

M.P. Kelly, Z.A. Conway, S.M. Gerbick, M. Kedzie, S.H. Kim, R.C. Murphy, B. Mustapha, P.N. Ostroumov, T. Reid
ANL, Argonne, USA

The set of seven new 72 MHz quarter wave SC (QWR) cavities has been completed and is being installed in the ATLAS heavy-ion accelerator at Argonne. The aim is to provide at least 17.5 MV accelerating potential with large acceptance and minimal beam losses for high intensity ion beams. The cavity electromagnetic design uses optimizations not used before with QWR including a large taper on both the inner and outer conductors in order to reduce surface fields and make efficient use of space along the beam line. Electropolishing (EP) on the finished cavities with integral helium jacket and no demountable RF joints has been performed, and is the first for any low beta SC cavity. This type of EP, adapted from Argonne systems for the linear collider effort, appears to have a large benefit in terms of the average quench field which range between 103-165 mT for five QWR tested to date. Cavity residual resistances at the proposed operating point of ~70 mT are low, clustering close to a value of ~2nOhm. Additional technical details including the almost exclusive use of wire EDM for niobium fabrication and a new CW 4 kW RF power coupler are presented.

Slides THIOC01 [10.152 MB]

THIOD03

Cavity Development for the Linear IFMIF Prototype Accelerator

cavity, cryomodule, simulation, SRF

878

N. Bazin, P. Carbonnier, G. Devanz, G. Disset, N. Grouas, P. Hardy, F. Orsini, D. Roudier
CEA/DSM/IRFU, France
J. Neyret
CEA/IRFU, Gif-sur-Yvette, France

The Linear IFMIF Prototype Accelerator (LIPAc), which is presently under design and realization, aims to accelerate a 125 mA deuteron beam up to 9 MeV. Therefore, a low-beta 175 MHz Half-Wave Resonator (HWR) was initially designed and manufactured with a tuning system based on a capacitive plunger located in the electric field region. Following the results of the vertical tests at 4.2K, this tuning system was abandoned and replaced by a conservative solution based on the HWR wall deformation using an external mechanical tuner. This paper will focus on the manufacturing of the prototype cavity, the studies realized to explain the first test results and the solutions taken to overcome the difficulties, leading to the validation of the prototype. Then, we will present the new cavity design.

Slides THIOD03 [8.845 MB]

THP002

Design of 3-Cell Travelling Wave Cavity for High Gradient Test

cavity, accelerating-gradient, feedback, pick-up

892

P.V. Avrakhov, A. Kanareykin, R.A. Kostin, Y. Xie
Euclid TechLabs, LLC, Solon, Ohio, USA
S. Kazakov, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, USA

Utilization of a superconducting traveling wave accelerating (STWA) structure with small phase advance per cell for future high energy linear colliders may provide accelerating gradient 1.2/1.4 times larger [1] than standing wave structure. However, the STWA structure requires a feedback waveguide [1]. Recent tests of 1.3 GHz model of a single-cell cavity with waveguide feedback demonstrated an accelerating gradient comparable to the gradient in a single-cell ILC-type cavity from the same manufacturer [2]. In the present paper a design for a STWA resonator with a 3-cell accelerating cavity for high gradient tests is considered. Methods to create and support the traveling wave in this structure are discussed. The results of detailed studies of the mechanical and tuning properties of the superconducting resonator with 3-cell traveling wave accelerating structure are also presented.

THP011

Improving Gradient of 9-cell SRF Cavities at Peking University

cavity, SRF, accelerating-gradient, electron

914

J.K. Hao, J.E. Chen, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, F. Wang, H.M. Xie, B.C. Zhang, K. Zhao, F. Zhu
PKU, Beijing, People's Republic of China

Four 9-cell TESLA superconducting cavities have been fabricated with Ningxia OTIC niobium material, including two fine grain and two large grain niobium cavities. The cavities have been tested after post treatments. At the early stage (PKU1 and PKU2), the gradient was about 23 MV/m. The gradient of PKU3 reached 28.4 MV/m, but the Q is low. The newest large grain 1.3 GHz 9-cell TESLA type SRF cavity (PKU4) has been made with careful control of machining, and improved surface treatment and electron beam welding. The maximum of gradient is 32.4 MV/m and the intrinsic quality factor (Q0) is 1.3x10¹⁰, which meet the requirement for ILC both in accelerating gradient and intrinsic quality factor.

THP016

DEVELOPMENT OF THE SUPERCONDUCTING HALF WAVE RESONATOR FOR INJECTOR II IN C-ADS

cavity, simulation, linac, proton

923

W.M. Yue, W. Chang, S. He, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, F.F. Wang, R.X. Wang, M.X. Xu, C. Zhang, S.H. Zhang, S.X. Zhang
IMP, Lanzhou, People's Republic of China

The Development of the Half Wave Resonator (HWR010) is based on the China ADS. The HWR010 operates at 162.5 MHz and can provide more than 0.78 MV of accelerating voltage per cavity for proton withβopt=0.10. We have designed the HWR010 in 2011. A copper model has been fabricated to test the HWR fabrication procedure. Five HWR010s have been fabricated in 2012. The HWR010s has finished the vertical testing and the Q0 is 4·10⁸ at Epeak = 45 MeV/m, and one of the HWR010s has been vertical tested with helium vessel. The slow tuner and high power coupler for this HWR have been developed and tested.

THP022

DEVELOPMENT OF A VERY LOW BETA SUPERCONDUCTING SINGLE SPOKE CAVITY FOR CHINA-ADS LINAC*

cavity, accelerating-gradient, linac, LLRF

942

H. Li, J.P. Dai, L.H. Li, H.Y. Lin, Q. Ma, W.M. Pan, Y. Sun, Q.Y. Wang, J. Zhang
IHEP, Beijing, People's Republic of China
H. Huang, P. Sha
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China

Twelve very low Beta superconducting single spoke cavities whose Beta is only 0.12 (Spoke012) operating at 325MHz, are adopted in Injector I for China-ADS linac. This type of spoke cavity is believed to be one of the key challenges for its very low geometric Beta. So far, collaborated with Peking University and Harbin Institute of Technology, IHEP has designed, fabricated and tested the spoke012 prototype cavity successfully. This paper presents the details of the design, fabrication and vertical test results for Spoke012 prototype cavity.

THP030

Superconducting RF Cavity Development With UK Industry

cavity, SRF, multipactoring, accelerating-gradient

966

A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C.A. Cooper, C.M. Ginsburg, A. Grassellino, O.S. Melnychuk, A.M. Rowe, D.A. Sergatskov
Fermilab, Batavia, USA
J.R. Everard, N. Shakespeare
Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom

As part of a continuing STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures Daresbury Laboratory and Shakespeare Engineering Ltd are developing the capability to fabricate, process and test a niobium 9-cell 1.3 GHz superconducting RF cavity. A single-cell cavity fabricated under this grant was surface processed and tested at Fermilab, and achieved an accelerating gradient in excess of 40 MV/m at an unloaded quality factor in excess of 1.0 x 10¹⁰. This paper presents the results of the single-cell cavity testing and discusses the progress made to date in the development of the design and manufacture of a 9-cell niobium cavity, which Shakespeare Engineering Ltd will fabricate and which is anticipated to be qualified in 2014.

THP038

Development and Performance of a High Field TE-Mode Sample Host Cavity

cavity, simulation, resonance, SRF

985

D.L. Hall, M. Liepe, I.S. Madjarov, K.P. McDermott, N.R.A. Valles
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: US National Science Foundation Career award PHY-0841213
A TE-mode 4 GHz sample host cavity has been designed and constructed at Cornell for the purpose of testing wafers of niobium and other candidates for the construction of SRF cavities. Simulations made using CLANS and ACE3P indicate that the peak magnetic field on the sample plate will reach approximately 120 mT before a quench occurs on the surface of the cavity due to thermal runaway. This quench field can be further increased using a 1400 C treatment to improve the thermal conductivity of the niobium bulk and a 120 C treatment to minimise the BCS surface resistance of the cavity walls. Such an improvement would put peak fields of 170 mT within reach of this cavity. Results of the cavity design, fabrication and first vertical test are presented and discussed.
*Development of Superconducting RF Sample Host Cavities and study of Pit-Induced Cavity Quench, Yie Xie, PhD Thesis, Cornell University, Jan 2013

THP084

The Tuning System for the HIE-ISOLDE High-Beta Quarter Wave Resonator

cavity, simulation, controls, LLRF

1121

P. Zhang, L. Alberty, L. Arnaudon, K. Artoos, S. Calatroni, O. Capatina, A. D'Elia, Y. Kadi, I. Mondino, T. Renaglia, D. Valuch, W. Venturini Delsolaro
CERN, Geneva, Switzerland
A. D'Elia
UMAN, Manchester, United Kingdom

Funding: Work supported in part by a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI.
A new linac using superconducting quarter-wave resonators (QWR) is under construction at CERN in the framework of the HIE-ISOLDE project. The QWRs are made by Niobium sputtered on a bulk Copper substrate. The working frequency at 4.5 K is 101.28 MHz and they will provide 6 MV/m accelerating gradient on the beam axis with a total maximum power dissipation of 10 W on cavity walls. A tuning system is required in order to both minimize the forward power variation in beam operation and to compensate the unavoidable uncertainties in the frequency shift during the cool-down process. The tuning system has to fulfill a complex combination of RF, structural and thermal requirements. The paper presents the functional specifications and details the tuning system RF and mechanical design and simulations. The results of the tests performed on a prototype system are discussed and the industrialization strategy is presented in view of final production.

FRIOA03

Fabrication and Testing of Deflecting Cavities for APS

cavity, operation, coupling, SRF

1170

J.D. Mammosser
JLab, Newport News, Virginia, USA
P. Dhakal, J. Henry, R.A. Rimmer, H. Wang, K.M. Wilson
JLAB, Newport News, Virginia, USA
J.F. Fuerst, J.P. Holzbauer, J.S. Kerby, A. Nassiri, G.J. Waldschmidt, G. Wu, Y. Yang
ANL, Argonne, USA
F. He
PKU, Beijing, People's Republic of China
Z. Li
SLAC, Menlo Park, California, USA

Abstract Jefferson Lab in Newport News, Virginia, in collaboration with Argonne National Laboratory, Argonne, Il, has fabricated and tested three production, 2.815 GHz crab cavities for Argonne’s Short-Pulse X-ray project. These cavities are unique in that the cavity and waveguides were milled from bulk large grain niobium ingot material directly from 3D CAD files. No forming of sub components was used with the exception of the beam-pipes. The cavity and helium vessel design along with the RF performance requirements makes this project extremely challenging for fabrication. Production challenges and fabrication techniques as well as testing results will be discussed in this paper.

Slides FRIOA03 [22.677 MB]

FRIOB02

Development and Performance of 325 MHz Single Spoke Resonators for Project X

cavity, operation, vacuum, electron

1187

L. Ristori, M.H. Awida, P. Berrutti, C.M. Ginsburg, I.V. Gonin, T.N. Khabiboulline, M. Merio, T.H. Nicol, D. Passarelli, A.M. Rowe, D.A. Sergatskov, A.I. Sukhanov, V.P. Yakovlev
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
Two types of single spoke resonators will be utilized for beam-acceleration in the low energy part of the Project X linac. SSR1 and SSR2 operate at 325 MHz and at an optimal beta of 0.22 and 0.51 respectively. After the initial phase of prototyping, a production run of 10 SSR1 resonators was recently completed in US industry. The qualification of this group of resonators in the Fermilab VTS is proceeding successfully and nearly complete. The first qualified resonator has been outfitted with a Stainless Steel helium vessel. Preliminary test results for the first jacketed SSR1 are presented. The first RF power couplers were ordered, the design of the double-lever tuning mechanism is almost complete.

Slides FRIOB02 [8.800 MB]

FRIOB04

CERN Developments for 704 MHz Superconducting Cavities

cavity, operation, linac, proton

1198

O. Capatina, G. Arnau-Izquierdo, S. Atieh, I. Aviles Santillana, R. Bonomi, S. Calatroni, J.K. Chambrillon, R. Garoby, F. Gerigk, M. Guinchard, T. Junginger, M. Malabaila, L. Marques Antunes Ferreira, S. Mikulas, V. Parma, T. Renaglia, K.M. Schirm, T. Tardy, M. Therasse, A. Vacca, N. Valverde Alonso, A. Vande Craen
CERN, Geneva, Switzerland
F. Pillon
Kraftanlagen Nukleartechnik GmbH, Heidelberg, Germany

The Superconducting Proton Linac (SPL) is an R&D effort coordinated by CERN in partnership with other international laboratories. It is aiming at developing key technologies for the construction of a multi-megawatt proton linac based on state-of-the-art RF superconducting technology, which would serve as a driver in new physics facilities for neutrinos and/or Radioactive Ion Beam (RIB). Amongst the main objectives of this R&D effort, is the development of 704 MHz bulk niobium β=1 elliptical cavities, operating at 2 K with a maximum accelerating gradient of 25 MV/m, and the testing of a string of cavities integrated in a machine-type cryomodule. The cavity together with its helium tank had to be carefully designed in coherence with the innovative design of the cryomodule. New fabrication methods have also been explored. Five such niobium cavities and two copper cavities are in fabrication. The key design aspects are discussed, the results of the alternative fabrication methods presented and the status of the cavity manufacturing and surface preparation is detailed.

Slides FRIOB04 [8.677 MB]

FRIOC01

Design of the 352 MHz, Beta 0.50, Double-Spoke Cavity for ESS

cavity, cryomodule, simulation, operation

1212

P. Duchesne, S. Bousson, S. Brault, P. Duthil, G. Olry, D. Reynet
IPN, Orsay, France
S. Molloy
ESS, Lund, Sweden

The ESS proton accelerator contains a superconducting sector consisting in three families of superconducting radiofrequency (SRF) bulk niobium cavities, operating at a nominal temperature of 2K: a family of Spoke cavities for the medium energy section followed by two families of elliptical cavities for higher energies. The superconducting Spoke section, having a length of 58.6m, consists of 14 cryomodules, each of them housing two 352.2 MHz β=0.50 Double-Spoke Resonators (DSR). The operating accelerating field is 8MV/m. The choice of the Spoke technology is guided by the high performances of such structures. Benefitting from 10 years of extensive R&D experience carried out at IPNO, the electromagnetic design studies came out with a solution that fulfills requirements of beam dynamics analysis and manufacturing considerations. Pursuing the same objective, the mechanical design of the cavity and its helium vessel were optimized by performing intensive coupled RF-mechanical simulations. We propose to present a review of the RF and mechanical design studies of the Spoke cavity. We will conclude with the integration of the Spoke cavity with its ancillaries inside the cryomodule.

Slides FRIOC01 [6.321 MB]