SRF2013 - List of Keywords (simulation)

Paper	Title	Other Keywords	Page
MOP018	Design of the MYRRHA 17-600 MeV Superconducting Linac	linac, cavity, lattice, operation	129
	J.-L. Biarrotte IPN, Orsay, France F. Bouly CERN, Geneva, Switzerland J.-P. Carneiro Fermilab, Batavia, USA D. Uriot CEA/DSM/IRFU, France D. Vandeplassche SCK•CEN, Mol, Belgium
	Funding: This work is being supported by the European Atomic Energy Community’s (EURATOM) Seventh Framework Programme under grant agreement n°269565 (MAX project). The goal of the MYRRHA project is to demonstrate the technical feasibility of transmutation in a 100MWth Accelerator Driven System (ADS) by building a new flexible irradiation complex in Mol (Belgium). The MYRRHA facility requires a 600 MeV accelerator delivering a maximum proton flux of 4 mA in continuous operation, with an additional requirement for exceptional reliability. This paper will briefly describe the beam dynamics design of the main superconducting linac section which covers the 17 to 600 MeV energy range and requires enhanced fault-tolerance capabilities.

TUIOA02	High Q0 Research: The Dynamics of Flux Trapping in Superconducting Niobium	cavity, niobium, experiment, 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]

TUIOA06	Research on Field Emission and Dark Current in ILC Cavities	electron, cavity, photon, detector	392
	Y.M. Li, K.X. Liu PKU, Beijing, People's Republic of China R.L. Geng, 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. Field emission and dark current are issues of concern for SRF cavity performance and SRF linac operation. Complete understanding and reliable control of the issue are still needed, especially in full-scale multi-cell cavities. Our work aims at developing a generic procedure for finding an active field emitter in a multi-cell cavity and benchmarking the procedure through cavity vertical test. Our ultimate goal is to provide feedback to cavity preparation and cavity string assembly in order to reduce or eliminate filed emission in SRF cavities. Systematic analysis of behaviors of field emitted electrons is obtained by ACE3P developed by SLAC. Experimental benchmark of the procedure was carried out in a 9-cell cavity vertical test at JLab. The energy spectrum of Bremsstrahlung X-rays is measured using a NaI(Tl) detector. The end-point energy in the X-ray energy spectrum is taken as the highest kinetic electron energy to predict longitudinal position of the active field emitter. Angular location of the field emitter is determined by an array of silicon diodes around irises of the cavity. High-resolution optical inspection was conducted at the predicted field emitter location.
	Slides TUIOA06 [4.565 MB]

TUP009	Magnetic Dependence of the Energy Gap: a Good Model to Fit Q Slope of Low Beta Cavities	cavity, superconductivity, experiment, niobium	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, niobium, 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.

TUP037	Dynamic Hardening Rule; a Generalization of the Classical Hardening Rule for Crystal Plasticity	experiment, SRF, controls, niobium	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.

TUP047	Niobium Cavity Electropolishing Modelling and Optimisation	cathode, SRF, cavity, niobium	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.

TUP068	Laser Polishing of Niobium for SRF Applications	laser, niobium, experiment, SRF	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]

TUP090	Thermal Simulations for the Multi-Layer Coating Model	feedback, electromagnetic-fields, superconducting-cavity, cavity	674
	F. Meng IHEP, Beijing, People's Republic of China A. Romanenko Fermilab, Batavia, USA Y. Xie Euclid TechLabs, LLC, Solon, Ohio, USA
	Thermal simulations for the multi-layer coating model has been developed based on previous work of a finite difference thermal feedback code.* RF field-attenuation formula for the multi-layer coating model has also been included.** The temperature distribution along different superconducting layers under applied magnetic fields has been calculated with various superconducting material parameters. Y. Xie et.al., "Relationship between defects pre-heating and defects size", SRF2009. *T. Kubo et.al.,"Rf field-attenuation formulae for the multilayer coating model", IPAC2013

TUP092	MUSICC3D: a Code for Modeling the Multipacting	cavity, electron, RF-structure, vacuum	683
	T. Hamelin, M. Chabot, J.-L. Coacolo, J. Lesrel, G. Martinet IPN, Orsay, France
	IPNO has conducted an effort to develop a 3D code for modeling multipacting in RF structures. The MUSICC3D program is using particle in cell method. Based on Runge Kutta method and using relativistic equation of motion, it solves the trajectory of a particle (e-) in the RF field. The integrations over the multi differential Secondary Emission Yield (SEY) (E_in, Alpha_in ,E_out, Alpha_out)) is made with Montecarlo method. Two running modes are available. The first one is using a model of virtual particle (i.e. the charge of a unique particle “rebounding” in the interior of the cavity is made by the product of SEYs occurring at each interaction with the walls). The other one makes generation of a full cascade of individual electrons. Benchmarking calculations have been done with analytical calculations and 2D particle in cell code (MULTIPAC). In all these cases the effects of the different inputs for the multi differential SEY have been investigated. Its intend is to give a guide to determine which precision on the SEY is needed to perform accurate multipacting calculations. Benchmarking with real cavity has been recently started and results with QWR Spiral2 cavities are presented. Hatch, Multipacting Modes etc., Physical Review. Wood, Investigations into Multipactor Breakdown etc., ESA Journal. Geng, Multipacting Simulations etc., Particule Accelerator Conference.

TUP112	Time-Resolved Measurements of High-Field Quench in SRF Cavities	cavity, SRF, niobium, 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.

WEIOD02	Magnetic Shielding: Our Experience with Various Shielding Materials	shielding, cryogenics, superconducting-RF, linac	808
	M. Masuzawa, A. Terashima, K. Tsuchiya KEK, Ibaraki, Japan A. Daël, O. Napoly, J. Plouin CEA/DSM/IRFU, France
	Magnetic shielding is a key technology for superconducting RF cavities. The tolerance of the ambient magnetic field depends on factors such as the operating RF frequency and acceleration gradient, but it can be as small as a few mG. Some high-Ni-content alloys, such as Cryperm 10 or Cryophy, which are claimed to maintain high permeability at cryogenic temperatures where superconducting cavities are operated, are commercially available at present and are used for magnetic shielding of superconducting cavities at many laboratories. Permeability measurements were made in order to understand the characteristics of such materials at both room and cryogenic temperatures, and the results will be used as a database for designing magnetic shields. It was found that the catalog performance of such materials was not always reproduced in the measurements. Some degradation was observed which depended on how the material was handled. The results of investigation into possible causes for the performance degradation of the shielding material at cryogenic temperature will be presented, along with permeability measurement results for various materials at different temperatures.
	Slides WEIOD02 [8.475 MB]

THIOD03	Cavity Development for the Linear IFMIF Prototype Accelerator	cavity, niobium, cryomodule, 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]

THIOD04	A Cold Tuner System With Mobile Plunger	cavity, linac, insertion, cryomodule	884
	D. Longuevergne, S. Blivet, S. Bousson, N. Gandolfo, G. Martinet, G. Olry, H. Saugnac IPN, Orsay, France
	Tuner systems for accelerating cavities are required to compensate static and dynamic frequency perturbations during beam operation. In the case of superconducting cavities, these are commonly tuned by deforming the cavity wall in specific places of the geometry. Nevertheless, considering the mechanical properties and frequency versus displacement sensitivity of some structures, tuning by deformation doesn’t allow to meet the requirements. In these specific cases, inspired from the “room temperature technology”, an alternative tuning technique by insertion of a helium-cooled superconducting plunger can be considered and has been studied for several projects (IFMIF, ESS-BILBAO). Advantages and drawbacks of such solution will be discussed and the successful results on SPIRAL2 cryomodule developed at IPNO will be presented.
	Slides THIOD04 [4.938 MB]

THP004	Design Progress of SSR1 Single Spoke Resonator for RAON	cavity, superconducting-cavity, acceleration, operation	899
	H.J. Cha, D. Jeon, H.C. Jung, H.J. Kim, G.-T. Park IBS, Daejeon, Republic of Korea R.E. Laxdal, Z.Y. Yao, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	Funding: The Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2011-032011 An advanced heavy ion accelerator for basic sciences and multiple applications, called “RAON”, is under construction in Daejeon, South Korea. The fabrication of prototypes for four different types of superconducting cavities, QWR, HWR, SSR1 and SSR2, is scheduled based on the on-going technical designs. In this paper, we present the electromagnetic and mechanical analyses for the SSR1 cavity (β=0.3 and f=325 MHz). Several variants have been considered and compared in terms of rf parameters, multipacting sensitivity, helium pressure sensitivity and ease of fabrication. This includes an analysis of stiffening rings and helium jacket design for stable operation. The progress towards the design of the SSR1 cavity will be given.

THP016	DEVELOPMENT OF THE SUPERCONDUCTING HALF WAVE RESONATOR FOR INJECTOR II IN C-ADS	cavity, niobium, 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.

THP017	Mechanical Study on the Cavity Package of 1.3 GHz Superconducting Accelerating Unit at IHEP	cavity, cryomodule, SRF, operation	926
	S. Jin, J. Gao, Z.C. Liu, J.Y. Zhai, H.J. Zheng IHEP, Beijing, People's Republic of China
	The program of 1.3GHz Superconducting RF (SRF) Accelerating Unit is under study at IHEP. A scheme of the unit structure is shown as fig. 1. In the unit, a 9-cell SRF cavity, tuner and a liquid helium (LHe) tank including a section of 50mm long, 0.3mm thick bellows will be welded and assembled together to form a relatively independent component called cavity package. In the study, mechanical analyses are carried out focusing on the package to assure its safety in the fabrications or other room temperature measurements. A commercial program of ANSYS Workbench is used.

THP018	Design of a Superconducting 352MHz Fully Jacketed Double-Spoke Resonator for the ESS-Bilbao Proton Linac	cavity, linac, cryomodule, DTL	929
	T. Junquera Accelerators and Cryogenic Systems, Orsay, France F.J. Bermejo, J.L. Muñoz, A.V. Vélez ESS Bilbao, Bilbao, Spain P. Duchesne, G. Olry IPN, Orsay, France
	The baseline design for the ESS-Bilbao light-ion linear accelerator and neutron source (a facility compliant with the ESS-AB requirements) has been completed and the normal conducting section of the linac (RFQ and DTL) is at present under detailed design and construction. Starting at 50 MeV, it is proposed to follow this section with a superconducting section composed of double and triple spoke cavities grouped in cryomodules of 2 or 3 cavities reaching a maximum energy of 300 MeV. After an initial R&D program on spoke cavities with an aluminum model, detailed electromagnetic and mechanical studies of a beta 0.50, 352MHz, double spoke cavity were performed. The results of the calculations are presented in this paper. It is proposed to continue this development by the construction and test of the niobium cavities prototypes and initiating the study of a cryo-module with two cavities that could be tested with beam at the ESS-Bilbao facility.

THP020	Measuring the Higher Order Mode Spectrum of the TRIUMF 9-cell Cavity	cavity, dipole, HOM, TRIUMF	936
	P. Kolb, B. Amini, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	The ARIEL eLINAC consists of five nine cell cavities, produced by PAVAC, and will accelerate 10 mA electrons to 50 MeV. This 500 kW beam will be used for rare isotope production. Future upgrade plans include a recirculating beam line. Recirculating the beam, for either energy doubling or energy recovery to drive a FEL, brings the risk of multi-pass beam break up (BBU). Therefore it is necessary to avoid higher order modes (HOMs) with high shunt impedance. The goal of the cavity design is to reduce the highest shunt impedance of any dipole HOM to 1 *10⁶Ω or less. Measurements on the nine cell cavity with bead pulling have been done to identify dipole modes and their geometric shunt impedance R/Q as well as measurements at 2 K to estimate the quality factor of those HOMs. Results of these measurements will be shown and compared to computer simulations done with ACE3P.

THP021	Design of the SSR021 Cavity for the Proton Accelerator Main Linac of China ADS	cavity, linac, proton, target	939
	Z.Q. Li, Y.L. Chi, Q. Ma, W.M. Pan, Y. Sun, J.Y. Tang, Q.Y. Wang, B. Xu, X.Y. Zhang IHEP, Beijing, People's Republic of China Y. He, C. Zhang, S.H. Zhang, S.X. Zhang IMP, Lanzhou, People's Republic of China H.Y. Lin, P. Sha Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
	China ADS is a high intensity proton machine based on CW superconducting technology. It includes two injectors and one main linac. The Institute of High Energy Physics (IHEP) and the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS), are responsible for developing the main linac together. This paper introduces the physics and mechanical design of the single spoke resonator (SSR021, beta021 cavity), which is used for first section of the main linac.

THP024	Lorentz Force Detuning Simulations of Spoke Cavities With Different Stiffening Elements	cavity, radiation, vacuum, operation	946
	J.L. Muñoz, F.J. Bermejo ESS Bilbao, Zamudio, Spain
	Lorentz force detuning caused by radiation pressure on the Nb cavity walls is of concern in cavity design and operation since its magnitude can approach the cavity bandwidth. This effect can be reduced using pasive stiffening elements in the cavity. In this work, Lorentz force detuning has been studied by numerical simulations for spoke cavities. Different stiffening elements has been considered. Static and dynamic behaviour have been analyzed by means of 3D static and transient electromagnetic and mechanical coupled finite elements simulations.

THP026	Cage Cavity: A Low Cost, High Performance SRF Accelerating Structure	cavity, SRF, HOM, vacuum	950
	J. Noonan, T.L. Smith, M. Virgo, G.J. Waldschmidt ANL, Argonne, USA J.W. Lewellen LANL, Los Alamos, New Mexico, USA
	Funding: Funded by Office of Naval Research. Argonne National Laboratory is operated by UChicago-Argonne LLC for the Department of Energy The Cage Cavity is a new SRF cavity technology using tubes formed into the shape of a solid wall cavity then assembled into a closed volume. The theory is that the cage cavity will form a resonant cavity at RF frequencies below a critical frequency at which the cage structure behaves as a solid structure. Several cage cavity structures have been fabricated and measured that demonstrate good RF properties. Comparison of simulations and measurements for these structures will be discussed. More importantly, simulations have identified a new cage cavity configuration in which an SRF cage cavity’s quality factor is greater than 10exp10. The cage cavity must operate in a vacuum vessel which is also an RF cavity. By choosing the cage cavity resonant frequency to be decoupled from the vessel higher order resonances, simulations show that the cage cavity Q is ~95% of a solid wall SRF cavity. The Cage Cavity design, fabrication costs, and high order mode behavior have a number of advantages over solid wall cavities. However, the cage cavity also has limitations. The design and properties of the cage cavity will be discussed and compared with existing SRF cavities.

THP027	Multipactor Analysis of the HWR at RISP	cavity, electron, resonance, coupling	955
	G.-T. Park IBS, Daejeon, Republic of Korea
	We report on the progress of the HWR development at RISP. The multipaction of the HWR was studied using CST-PS (PIC) solver and multipacting band is predicted. Additional considerations were given to see the effects of the coupling ports and the coupler on the multipaction. We present the modified cavity design without multipaction at our operation accelerating voltage~1.2MV.

THP028	The Research on Spoke 0.40 Cavity	cavity, proton, linac, superconducting-cavity	959
	P. Sha, H. Huang Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China W.M. Pan, X.Y. Zhang IHEP, Beijing, People's Republic of China
	Spoke superconducting cavity can be used in the low-energy section of the proton accelerator. It has many significant advantages: compact structure, high value of R/Q, etc. The Chinese ADS (Accelerator Driven System) project will adopt many spoke cavities with 3 different β values (0.12, 0.21, 0.40). Spoke040 cavities (β=0.40) are used to increase the proton energy from 34 MeV to 178 MeV. Now the physical design of spoke040 cavity has been finished, and the machining are going on right now. The vertical test would be held at the end of this year.

THP029	Simulation of Mechanical Resonances of SRF Cavities in Low Beam Current CW Operation	cavity, resonance, operation, cryomodule	962
	N. Solyak, M.H. Awida, I.V. Gonin, T.N. Khabiboulline, Y.M. Pischalnikov, W. Schappert, V.P. Yakovlev Fermilab, Batavia, USA
	The low beam current for CW operation of the Project X requires cavities to be mechanically optimized to operate at a high loaded Q and thus, low bandwidth with higher sensitivity to microphonics. The essential source of microphonics detuning is fluctuations in the helium pressure df/dp. Last year’s several methods for reducing df/dp has been proposed. One of the other possible sources of RF frequency instability is mechanical resonances. The cavity could be driven out of operating frequency by the mechanical deformations due to vibrations caused by external factors. In this paper we present the COMSOL multiphysics algorithm developed for evaluation of operating frequency shift due to mechanical resonances in SC cavities. We discuss the results of simulations for 5-cell elliptical 650 MHz β=0.9 cavities. The comparison of COMSOL simulations and measurements of ILC type cavities in Horizontal Test Stand at Fermilab is presented.

THP031	Superconducting Test of the 56 MHz SRF Quarter Wave Resonator for RHIC	cavity, SRF, electron, resonance	969
	Q. Wu, S.A. Belomestnykh, I. Ben-Zvi, G.T. McIntyre, R. Porqueddu, S.K. Seberg, T. Xin BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. A 56 MHz superconducting RF cavity will be the first quarter wave resonator (QWR) installed in a high energy storage ring. It is expected to boost the luminosity of the Relativistic Heavy Ion Collider by more than 60% after installation. In this paper, we discuss the cavity parameters and design features. We report the results from the first vertical test of this cavity at 4 K.

THP033	Study of Balloon Spoke Cavities	cavity, TRIUMF, operation, proton	972
	Z.Y. Yao, R.E. Laxdal, B.S. Waraich, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada R. Edinger PAVAC, Richmond, B.C., Canada
	A balloon geometry has been proposed to suppress multipacting for single spoke resonators. The design may find a useful application for proton and ion accelerator projects. TRIUMF has completed initial RF, mechanical, and fabrication studies on this special geometry for both low (β=0.12) and medium (β=0.3) β geometries. The RF properties are comparable with that of traditional spoke cavities but with improved RF efficiency in addition to the reduced multipacting. The results of electro-magnetic and structural design studies comparing the balloon geometry with traditional spoke geometries will be presented. We will also present optimization studies of the mechanical design, such as decreasing df/dp by EM field compensation as well as discussing tuning strategies and fabrication techniques.

THP034	Multipacting Suppression in a Single Spoke Cavity	cavity, electron, resonance, operation	975
	Z.Y. Yao, R.E. Laxdal, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada X.Y. Lu, K. Zhao PKU, Beijing, People's Republic of China
	Spoke cavities are good candidates for the low and medium β section of a high intensity proton or ion accelerator. For many high intensity accelerators, stability and reliability are the most important properties. Currently, one of the key issues of spoke cavity performance is multipacting, which may cause instability during operation. Multipacting in a spoke cavity has a troublesome characteristic as it presents a continual barrier over a wide gradient range, usually in the range of operation from 3MV/m to 15MV/m. A good surface processing can improve the secondary electron emission yield. However, the complex 3D structure makes it not easily achievable as with the elliptical cavity variants. Suppressing multipacting in the design stage is clearly advantageous. This paper will present a multipacting study based on the PKU-I spoke cavity. A systematic correlation between geometric parameters and multipacting behaviors is obtained. Based on this study a new geometry of single spoke cavity called the ‘balloon’ variant is proposed.

THP038	Development and Performance of a High Field TE-Mode Sample Host Cavity	cavity, niobium, 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

THP039	Design of a Triple-Spoke Cavity as a Rebuncher for RIKEN RI-Beam Factory	cavity, factory, heavy-ion, acceleration	988
	L. Lu RIKEN, Saitama, Japan O. Kamigaito, N. Sakamoto, K. Suda, K. Yamada RIKEN Nishina Center, Wako, Japan
	A superconducting triple-spoke cavity as a rebuncher for very heavy ion beams such as uranium at β=0.303 for RIKEN RI-beam factory is designed. The required total gap voltage is 3 MV. In this design, thick ribs (25 mm) are placed on the both ends of cavity so that the deformation caused by pressure of liquid helium is less than 0.5 mm. A copper test model with one spoke is designed to be fabricated using the same technique as that for Nb cavity. The detailed design will be presented.

THP040	3D MULTIPACTING STUDY FOR THE ROSSENDORF SRF GUN	electron, gun, SRF, cathode	991
	E.T. Tulu, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany A. Arnold HZDR, Dresden, Germany
	Funding: *This work is supported by Federal Ministry for Research and Education BMBF Electron multipacting is still observed in the Rossendorf SRF gun which limits the cavity fields (accelerating gradient). To better understand this process, a three-cell 1.3 GHz elliptical-shape cavity with cathode was modeled in CST Studio Suite® 2013 at the University of Rostock. All parameters are provided by Helmholtz-Zentrum Dresden-Rossendorf. The multipacting simulations have been performed with CST Microwave Studio® (CST MWS) [1] and CST Particle Studio® (CST PS) which is suitable and powerful for 3D electromagnetic designs and provides the most advanced model of secondary emission. The radio frequency fields are calculated using the frequency domain solver of CST MWS, whereas the CST PS is used for particle tracking simulation [2]. The purpose of these numerical simulations is to better comprehend multipacting in the Rossendorf SRF gun and make a detailed analysis. The midterm goal is to find a new cavity shape, which might suppress the electron amplification so that the SRF Gun will be able to operate up to an accelerating gradient of 50 MV/m. #eden.tulu@uni-rostock.de [1] CST AG, Bad Nauheimer Str. 19, D-64289 Darmstadt, Germany [2] F. Hamme, U. Becker and P. Hammes, Proc. of ICAP 2006, Chamonix, France

THP042	High Frequency SRF Cavity Study for Bunch Shortening in PEPX	cavity, HOM, SRF, FEL	998
	L. Xiao, K.L.F. Bane, Y. Cai, X. Huang, C.-K. Ng, A. Novokhatski, L. Wang SLAC, Menlo Park, California, USA
	The proposed PEPX is a diffraction limited storage ring light source, or “ultimate storage ring (USR)”, which can be built in the PEP tunnel at SLAC. The 4.5GeV PEPX design based on the USR with a natural emittance about 10pm-rad can be used to drive a high-gain soft X-ray FEL. In order to achieve a desired high peak current over 300A for the FEL, the bunch length is reduced to 1ps from 10ps through a set of multi-cell SRF cavities working at 1.428GHz in CW mode, providing about 300MV RF gradient. In this paper, the 1.5GHz JLAB C100 cavity for the CEBAF upgrade and 1.3GHz Cornell ERL cavity are investigated for its application to PEPX-FEL. The simulation results show that the beam induced high order modes (HOM) in the C100 cavities will limit the threshold of the beam current for PEPX-FEL. And the same pass band modes (SPM) in the cavities are strongly trapped, and thus generate unacceptable beam power once they hit the beam resonances. Therefore, a 5-cell with a larger iris cavity design instead of the C100 7-cell design is proposed. Preliminary results on the rf parameters of the cavity, HOM damping and beam dynamics studies will be presented.

THP043	Design and Vertical Test of Double Quarter Wave Crab Cavity for LHC Luminosity Upgrade	cavity, cryogenics, pick-up, HOM	1002
	B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, R. Calaga, C. Cullen, L.R. Hammons, J. Skaritka, S. Verdú-Andrés, Q. Wu BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. DOE, and supported by EU FP7 HiLumi LHC - Grant Agreement 284404. A proof of principle Double Quarter Wave Crab Cavity (DQWCC) was designed and fabricated for the Large Hadron Collider (LHC) luminosity upgrade. Vertical cryogenic test has been done in Brookhaven National Lab (BNL). We report the test results of this design.

THP044	Compact Higher Order Mode Filter for Crab Cavities in the Large Hadron Collider	HOM, cavity, luminosity, cryomodule	1006
	B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, S. Verdú-Andrés, Q. Wu BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA R. Calaga CERN, Geneva, Switzerland
	Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. DOE, and supported by EU FP7 HiLumi LHC - Grant Agreement 284404. A double quarter wave crab cavity was designed for the Large Hadron Collider luminosity upgrade. Starting from the analytical calculation of simplified RLC circuit, a compact higher order mode filter is developed for this cavity. Finite element simulation results are presented. The design concept is generic and can easily be adapted to other cavities.

THP050	Development of Power Coupler for Superconducting Spoke Cavities for China ADS Proton Linac	cavity, vacuum, coupling, Windows	1024
	X. Chen, T.M. Huang, H.Y. Lin, Q. Ma, F. Meng, W.M. Pan, Y.H. Peng IHEP, Beijing, People's Republic of China
	Abstract: The China-ADS proton linac adopts β=0.12 superconducting Spoke cavities. Each cavity is powered via a 325MHz coaxial power coupler. The coupler is to feed 6kW maximum power though it is designed to handle at 15kW .Two coupler sets have been made by IHEP so far, and a 10kW RF power in continuous travelling wave mode has passed through the coupler during high power test in late January 2013. An introduction of this coupler design and the room temperature test results are presented in this paper.

THP058	Update on the European XFEL RF Power Input Coupler	cryogenics, superconductivity, linac, electron	1047
	D. Kostin, W.-D. Möller DESY, Hamburg, Germany W. Kaabi LAL, Orsay, France
	European XFEL project is being currently realized in Hamburg, Germany. The 1.5 km 17.5 GeV linear electron accelerator is based on the 1.3GHz 9-cell TESLA type SRF cavity. The RF power input coupler design for the E-XFEL is based on well known TTF3 coupler design, used in FLASH accelerator. Coupler design was adapted for the industrial production with some parameters optimisation revisited and simulations done. Results are presented and discussed.

THP059	HOM Coupler Design Adjustment for CW operation of the 1.3 GHz 9-cell TESLA Type SRF Cavity	HOM, dipole, cavity, operation	1051
	D. Kostin, W.-D. Möller, J.K. Sekutowicz DESY, Hamburg, Germany
	One of the key features of a modern research facility is its versatility, ability to adjust for a multitude of the applications and user needs. A challenge for the coming European XFEL is to become a multipurpose laboratory with a broad applications spectrum. Primarily, the XFEL is a pulsed machine. Encompassing the CW mode would be a worthy addition. CW operation of the 1.3GHz 9-cell TESLA Type SRF Cavity was performed several times at DESY and other Labs successfully. One of the difficulties was a heat load of the High Order Mode (HOM) couplers. To amend this HOM coupler design adjustement is proposed, simulated and modelled. Results are presented and discussed.

THP060	High Power RF Coupler for ADS Accelerating Cavities	cavity, operation, linac, Windows	1055
	S.V. Kutsaev, M.P. Kelly, B. Mustapha, J.A. Nolen, P.N. Ostroumov ANL, Argonne, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. Accelerator driven systems (ADS) require a high-power CW proton accelerator with proton beam energy near 1 GeV. High-gradient superconducting TEM-cavities are a natural choice for the front end of linac. This paper presents the design of superconducting low-beta half wave resonator operating at 162 MHz frequency for ADS, as well as a new 75 kW power coupler that has been designed at Argonne National Laboratory. This coupler would permit operations with an accelerating voltage of 3.0 MV with a beam current of 25 mA. The coupler includes a cold RF window which keeps the antenna at low temperature and a variable bellows section to adjust the coupling factor. The importance of these features for reliable operation will be discussed in detail.

THP061	Developments of HOM Dampers for SuperKEKB Superconducting Cavity	cavity, HOM, operation, factory	1058
	M. Nishiwaki, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, Y. Morita KEK, Ibaraki, Japan
	Eight superconducting accelerating cavities were stably operated under a high beam current and a large beam induced HOM power in KEKB electron ring. The HOM power of 16 kW at the beam current of 1.4A was absorbed in two ferrite dampers attached to each cavity. In SuperKEKB, that is the upgrade machine of KEKB, the design beam current is 2.60 A. The HOM power of higher than 40 kW is expected to be induced. To cope with the large HOM power, precise evaluations of HOM power loads including HOM dampers were carried out. Then, new ferrite dampers with reinforced water cooling were developed and high-power tested. On the other hand, the evaluation indicated that an additional HOM damper can absorb significant amount of HOM power. Additional damper is effective to reduce each ferrite damper load. In this report, we will describe the results of high power tests of the new ferrite dampers, studies for additional dampers, and an installation plan for SuperKEKB.

THP062	Optimisation of the 3-Stub Tuner for Matching the Diamond SCRF Cavities	cavity, operation, coupling, storage-ring	1061
	S.A. Pande, C. Christou, P. Gu, M. Jensen Diamond, Oxfordshire, United Kingdom
	The Diamond Storage Ring cavities are aperture coupled resulting in a fixed external Q. This results in the cavities being matched under certain conditions depending on the loss per turn, the beam current and the accelerating voltage. Operationally, there are advantages to limiting the accelerating voltage to improve reliability and lifetime, which at high beam current results in a mismatch and high reflected power. To match the cavities under such non-optimum operating conditions we use 3-stub tuners in the waveguide feeds. It has been observed, that certain configurations of the 3-stub tuners can improve the match of the cavity, but this can result in strong heating of the waveguide in the cryostat. Numerical simulations of the cavity along with the coupling waveguide and 3-stub tuners have been carried out using CST Studio for different beam loading conditions to optimise the 3-stub tuners for acceptable match and heating. In this paper we present the results of our simulations and comparisons with measurements for operation with different beam currents and cavity voltages.

THP066	SARAF Phase-I HWR Coupler Cooling Design	operation, linac, cavity, proton	1073
	J. Rodnizki, Y. Ben Aliz, I. Fishman, A. Grin, Z. Horvitz, B. Kaizer, L. Weissman Soreq NRC, Yavne, Israel
	The Soreq Applied Research Accelerator Facility (SARAF) design is based on a 40 MeV 5 mA light ions superconducting RF linac. Phase I of SARAF delivers up to 2 mA CW proton beam in an energy range of 1.5-4.5 MeV. The maximum beam power that we have reached is 4.5 kW. The warming of the SARAF linac RF couplers is currently the main limiting factor for reaching higher CW beam power. The coupler cooling configuration was optimized by increasing the cold window copper braid and adding a copper braid to the top end, using CST Multiphysics and ANSYS steady state and transient solvers. The study was conducted for the heat load generated by the surface currents of a matched 4 kW forward CW power, simulated by the CST MWS FD solver. Multipacting is a known potential heat source that overheats the coupler in the vicinity of the cold window. The coupler overheat phenomena was experimentally studied as a function of DC bias voltage, and it was found that a 900 V bias reduces significantly the heating rate. As a result we expect that the beam power can be significantly increased. The long overheat period implies that optimization of the cooling configuration is still needed.

THP068	New Design of HOM Coupler Using Coaxial-like Rounded Waveguide	HOM, cavity, damping, operation	1081
	M. Sawamura Japan Atomic Energy Agency (JAEA), Gamma-ray Non-Destructive Assay Research Group, Tokai-mura, Ibaraki-ken, Japan R. Hajima, R. Nagai, N. Nishimori JAEA, Ibaraki-ken, Japan
	It is important to damp higher-order modes (HOMs) of superconducting accelerators especially for energy-recovery linacs of high current operation. Though various types of HOM couplers, beam line HOM dampers and waveguide HOM couplers have been developed, there are some problems such as inner conductor heating of output connector for HOM couplers and low packing factor for beam line HOM dampers. We propose new design of HOM coupler. This coupler consists of a coaxial line coupled with a cavity or a beam pipe and a rounded waveguide which cuts off the accelerating mode. The rounded waveguide is similar to a coaxial line and the inner conductor and outer conductor are connected with a plate which corresponds to waveguide side wall. This enables the inner connector cooled down efficiently through the outer conductor. The calculation results of MW-STUDIO will be presented.

THP077	Coaxial Blade Tuner for European XFEL 3.9 GHz cavities	cavity, linac, operation, cryomodule	1101
	R. Paparella, M. Bertucci, A. Bosotti INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	The European XFEL linac injector features a third harmonic section jointly realized by INFN and DESY and hosting a 3.9 GHz 9-cell cavities cryomodule. The cold tuning system, developed by INFN for these cavities, is inspired by the coaxial Blade Tuner already qualified for ILC cavities. Design, fabrication and room temperature qualification of first tuner units produced are reviewed in this paper.

THP084	The Tuning System for the HIE-ISOLDE High-Beta Quarter Wave Resonator	cavity, niobium, 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.

THP095	Error Analysis for Vertical Test Stand Cavity Measurements at Fermilab	cavity, detector, resonance, SRF	1148
	O.S. Melnychuk Fermilab, Batavia, USA
	Overview of Vertical Test Stand (VTS) facility at Fermilab is presented. Uncertainty calculations for the measurements of quality factor and accelerating field are described Sources of uncertainties and assumptions on their correlations are reviewed. VTS hardware components with non-negligible instrumental errors are discussed. Relative contributions of individual sources to the total uncertainties are assessed. Stability of VTS test results with respect to potential mismeasurements of calibration coefficients and decay constant are studied.

FRIOC01	Design of the 352 MHz, Beta 0.50, Double-Spoke Cavity for ESS	cavity, cryomodule, operation, niobium	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]

Paper

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Other Keywords

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MOP018

Design of the MYRRHA 17-600 MeV Superconducting Linac

linac, cavity, lattice, operation

129

J.-L. Biarrotte
IPN, Orsay, France
F. Bouly
CERN, Geneva, Switzerland
J.-P. Carneiro
Fermilab, Batavia, USA
D. Uriot
CEA/DSM/IRFU, France
D. Vandeplassche
SCK•CEN, Mol, Belgium

Funding: This work is being supported by the European Atomic Energy Community’s (EURATOM) Seventh Framework Programme under grant agreement n°269565 (MAX project).
The goal of the MYRRHA project is to demonstrate the technical feasibility of transmutation in a 100MWth Accelerator Driven System (ADS) by building a new flexible irradiation complex in Mol (Belgium). The MYRRHA facility requires a 600 MeV accelerator delivering a maximum proton flux of 4 mA in continuous operation, with an additional requirement for exceptional reliability. This paper will briefly describe the beam dynamics design of the main superconducting linac section which covers the 17 to 600 MeV energy range and requires enhanced fault-tolerance capabilities.

TUIOA02

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

cavity, niobium, experiment, 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]

TUIOA06

Research on Field Emission and Dark Current in ILC Cavities

electron, cavity, photon, detector

392

Y.M. Li, K.X. Liu
PKU, Beijing, People's Republic of China
R.L. Geng, 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.
Field emission and dark current are issues of concern for SRF cavity performance and SRF linac operation. Complete understanding and reliable control of the issue are still needed, especially in full-scale multi-cell cavities. Our work aims at developing a generic procedure for finding an active field emitter in a multi-cell cavity and benchmarking the procedure through cavity vertical test. Our ultimate goal is to provide feedback to cavity preparation and cavity string assembly in order to reduce or eliminate filed emission in SRF cavities. Systematic analysis of behaviors of field emitted electrons is obtained by ACE3P developed by SLAC. Experimental benchmark of the procedure was carried out in a 9-cell cavity vertical test at JLab. The energy spectrum of Bremsstrahlung X-rays is measured using a NaI(Tl) detector. The end-point energy in the X-ray energy spectrum is taken as the highest kinetic electron energy to predict longitudinal position of the active field emitter. Angular location of the field emitter is determined by an array of silicon diodes around irises of the cavity. High-resolution optical inspection was conducted at the predicted field emitter location.

Slides TUIOA06 [4.565 MB]

TUP009

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

cavity, superconductivity, experiment, niobium

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, niobium, 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.

TUP037

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

experiment, SRF, controls, niobium

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.

TUP047

Niobium Cavity Electropolishing Modelling and Optimisation

cathode, SRF, cavity, niobium

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.

TUP068

Laser Polishing of Niobium for SRF Applications

laser, niobium, experiment, SRF

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]

TUP090

Thermal Simulations for the Multi-Layer Coating Model

feedback, electromagnetic-fields, superconducting-cavity, cavity

674

F. Meng
IHEP, Beijing, People's Republic of China
A. Romanenko
Fermilab, Batavia, USA
Y. Xie
Euclid TechLabs, LLC, Solon, Ohio, USA

Thermal simulations for the multi-layer coating model has been developed based on previous work of a finite difference thermal feedback code.* RF field-attenuation formula for the multi-layer coating model has also been included.** The temperature distribution along different superconducting layers under applied magnetic fields has been calculated with various superconducting material parameters.
*Y. Xie et.al., "Relationship between defects pre-heating and defects size", SRF2009.
**T. Kubo et.al.,"Rf field-attenuation formulae for the multilayer coating model", IPAC2013

TUP092

MUSICC3D: a Code for Modeling the Multipacting

cavity, electron, RF-structure, vacuum

683

T. Hamelin, M. Chabot, J.-L. Coacolo, J. Lesrel, G. Martinet
IPN, Orsay, France

IPNO has conducted an effort to develop a 3D code for modeling multipacting in RF structures. The MUSICC3D program is using particle in cell method. Based on Runge Kutta method and using relativistic equation of motion, it solves the trajectory of a particle (e-) in the RF field. The integrations over the multi differential Secondary Emission Yield (SEY) (E_in, Alpha_in ,E_out, Alpha_out)) is made with Montecarlo method. Two running modes are available. The first one is using a model of virtual particle (i.e. the charge of a unique particle “rebounding” in the interior of the cavity is made by the product of SEYs occurring at each interaction with the walls). The other one makes generation of a full cascade of individual electrons. Benchmarking calculations have been done with analytical calculations and 2D particle in cell code (MULTIPAC). In all these cases the effects of the different inputs for the multi differential SEY have been investigated. Its intend is to give a guide to determine which precision on the SEY is needed to perform accurate multipacting calculations. Benchmarking with real cavity has been recently started and results with QWR Spiral2 cavities are presented.
Hatch, Multipacting Modes etc., Physical Review.
Wood, Investigations into Multipactor Breakdown etc., ESA Journal.
Geng, Multipacting Simulations etc., Particule Accelerator Conference.

TUP112

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

cavity, SRF, niobium, 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.

WEIOD02

Magnetic Shielding: Our Experience with Various Shielding Materials

shielding, cryogenics, superconducting-RF, linac

808

M. Masuzawa, A. Terashima, K. Tsuchiya
KEK, Ibaraki, Japan
A. Daël, O. Napoly, J. Plouin
CEA/DSM/IRFU, France

Magnetic shielding is a key technology for superconducting RF cavities. The tolerance of the ambient magnetic field depends on factors such as the operating RF frequency and acceleration gradient, but it can be as small as a few mG. Some high-Ni-content alloys, such as Cryperm 10 or Cryophy, which are claimed to maintain high permeability at cryogenic temperatures where superconducting cavities are operated, are commercially available at present and are used for magnetic shielding of superconducting cavities at many laboratories. Permeability measurements were made in order to understand the characteristics of such materials at both room and cryogenic temperatures, and the results will be used as a database for designing magnetic shields. It was found that the catalog performance of such materials was not always reproduced in the measurements. Some degradation was observed which depended on how the material was handled. The results of investigation into possible causes for the performance degradation of the shielding material at cryogenic temperature will be presented, along with permeability measurement results for various materials at different temperatures.

Slides WEIOD02 [8.475 MB]

THIOD03

Cavity Development for the Linear IFMIF Prototype Accelerator

cavity, niobium, cryomodule, 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]

THIOD04

A Cold Tuner System With Mobile Plunger

cavity, linac, insertion, cryomodule

884

D. Longuevergne, S. Blivet, S. Bousson, N. Gandolfo, G. Martinet, G. Olry, H. Saugnac
IPN, Orsay, France

Tuner systems for accelerating cavities are required to compensate static and dynamic frequency perturbations during beam operation. In the case of superconducting cavities, these are commonly tuned by deforming the cavity wall in specific places of the geometry. Nevertheless, considering the mechanical properties and frequency versus displacement sensitivity of some structures, tuning by deformation doesn’t allow to meet the requirements. In these specific cases, inspired from the “room temperature technology”, an alternative tuning technique by insertion of a helium-cooled superconducting plunger can be considered and has been studied for several projects (IFMIF, ESS-BILBAO). Advantages and drawbacks of such solution will be discussed and the successful results on SPIRAL2 cryomodule developed at IPNO will be presented.

Slides THIOD04 [4.938 MB]

THP004

Design Progress of SSR1 Single Spoke Resonator for RAON

cavity, superconducting-cavity, acceleration, operation

899

H.J. Cha, D. Jeon, H.C. Jung, H.J. Kim, G.-T. Park
IBS, Daejeon, Republic of Korea
R.E. Laxdal, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

Funding: The Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2011-032011
An advanced heavy ion accelerator for basic sciences and multiple applications, called “RAON”, is under construction in Daejeon, South Korea. The fabrication of prototypes for four different types of superconducting cavities, QWR, HWR, SSR1 and SSR2, is scheduled based on the on-going technical designs. In this paper, we present the electromagnetic and mechanical analyses for the SSR1 cavity (β=0.3 and f=325 MHz). Several variants have been considered and compared in terms of rf parameters, multipacting sensitivity, helium pressure sensitivity and ease of fabrication. This includes an analysis of stiffening rings and helium jacket design for stable operation. The progress towards the design of the SSR1 cavity will be given.

THP016

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

cavity, niobium, 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.

THP017

Mechanical Study on the Cavity Package of 1.3 GHz Superconducting Accelerating Unit at IHEP

cavity, cryomodule, SRF, operation

926

S. Jin, J. Gao, Z.C. Liu, J.Y. Zhai, H.J. Zheng
IHEP, Beijing, People's Republic of China

The program of 1.3GHz Superconducting RF (SRF) Accelerating Unit is under study at IHEP. A scheme of the unit structure is shown as fig. 1. In the unit, a 9-cell SRF cavity, tuner and a liquid helium (LHe) tank including a section of 50mm long, 0.3mm thick bellows will be welded and assembled together to form a relatively independent component called cavity package. In the study, mechanical analyses are carried out focusing on the package to assure its safety in the fabrications or other room temperature measurements. A commercial program of ANSYS Workbench is used.

THP018

Design of a Superconducting 352MHz Fully Jacketed Double-Spoke Resonator for the ESS-Bilbao Proton Linac

cavity, linac, cryomodule, DTL

929

T. Junquera
Accelerators and Cryogenic Systems, Orsay, France
F.J. Bermejo, J.L. Muñoz, A.V. Vélez
ESS Bilbao, Bilbao, Spain
P. Duchesne, G. Olry
IPN, Orsay, France

The baseline design for the ESS-Bilbao light-ion linear accelerator and neutron source (a facility compliant with the ESS-AB requirements) has been completed and the normal conducting section of the linac (RFQ and DTL) is at present under detailed design and construction. Starting at 50 MeV, it is proposed to follow this section with a superconducting section composed of double and triple spoke cavities grouped in cryomodules of 2 or 3 cavities reaching a maximum energy of 300 MeV. After an initial R&D program on spoke cavities with an aluminum model, detailed electromagnetic and mechanical studies of a beta 0.50, 352MHz, double spoke cavity were performed. The results of the calculations are presented in this paper. It is proposed to continue this development by the construction and test of the niobium cavities prototypes and initiating the study of a cryo-module with two cavities that could be tested with beam at the ESS-Bilbao facility.

THP020

Measuring the Higher Order Mode Spectrum of the TRIUMF 9-cell Cavity

cavity, dipole, HOM, TRIUMF

936

P. Kolb, B. Amini, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

The ARIEL eLINAC consists of five nine cell cavities, produced by PAVAC, and will accelerate 10 mA electrons to 50 MeV. This 500 kW beam will be used for rare isotope production. Future upgrade plans include a recirculating beam line. Recirculating the beam, for either energy doubling or energy recovery to drive a FEL, brings the risk of multi-pass beam break up (BBU). Therefore it is necessary to avoid higher order modes (HOMs) with high shunt impedance. The goal of the cavity design is to reduce the highest shunt impedance of any dipole HOM to 1 *10⁶Ω or less. Measurements on the nine cell cavity with bead pulling have been done to identify dipole modes and their geometric shunt impedance R/Q as well as measurements at 2 K to estimate the quality factor of those HOMs. Results of these measurements will be shown and compared to computer simulations done with ACE3P.

THP021

Design of the SSR021 Cavity for the Proton Accelerator Main Linac of China ADS

cavity, linac, proton, target

939

Z.Q. Li, Y.L. Chi, Q. Ma, W.M. Pan, Y. Sun, J.Y. Tang, Q.Y. Wang, B. Xu, X.Y. Zhang
IHEP, Beijing, People's Republic of China
Y. He, C. Zhang, S.H. Zhang, S.X. Zhang
IMP, Lanzhou, People's Republic of China
H.Y. Lin, P. Sha
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China

China ADS is a high intensity proton machine based on CW superconducting technology. It includes two injectors and one main linac. The Institute of High Energy Physics (IHEP) and the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS), are responsible for developing the main linac together. This paper introduces the physics and mechanical design of the single spoke resonator (SSR021, beta021 cavity), which is used for first section of the main linac.

THP024

Lorentz Force Detuning Simulations of Spoke Cavities With Different Stiffening Elements

cavity, radiation, vacuum, operation

946

J.L. Muñoz, F.J. Bermejo
ESS Bilbao, Zamudio, Spain

Lorentz force detuning caused by radiation pressure on the Nb cavity walls is of concern in cavity design and operation since its magnitude can approach the cavity bandwidth. This effect can be reduced using pasive stiffening elements in the cavity. In this work, Lorentz force detuning has been studied by numerical simulations for spoke cavities. Different stiffening elements has been considered. Static and dynamic behaviour have been analyzed by means of 3D static and transient electromagnetic and mechanical coupled finite elements simulations.

THP026

Cage Cavity: A Low Cost, High Performance SRF Accelerating Structure

cavity, SRF, HOM, vacuum

950

J. Noonan, T.L. Smith, M. Virgo, G.J. Waldschmidt
ANL, Argonne, USA
J.W. Lewellen
LANL, Los Alamos, New Mexico, USA

Funding: Funded by Office of Naval Research. Argonne National Laboratory is operated by UChicago-Argonne LLC for the Department of Energy
The Cage Cavity is a new SRF cavity technology using tubes formed into the shape of a solid wall cavity then assembled into a closed volume. The theory is that the cage cavity will form a resonant cavity at RF frequencies below a critical frequency at which the cage structure behaves as a solid structure. Several cage cavity structures have been fabricated and measured that demonstrate good RF properties. Comparison of simulations and measurements for these structures will be discussed. More importantly, simulations have identified a new cage cavity configuration in which an SRF cage cavity’s quality factor is greater than 10exp10. The cage cavity must operate in a vacuum vessel which is also an RF cavity. By choosing the cage cavity resonant frequency to be decoupled from the vessel higher order resonances, simulations show that the cage cavity Q is ~95% of a solid wall SRF cavity. The Cage Cavity design, fabrication costs, and high order mode behavior have a number of advantages over solid wall cavities. However, the cage cavity also has limitations. The design and properties of the cage cavity will be discussed and compared with existing SRF cavities.

THP027

Multipactor Analysis of the HWR at RISP

cavity, electron, resonance, coupling

955

G.-T. Park
IBS, Daejeon, Republic of Korea

We report on the progress of the HWR development at RISP. The multipaction of the HWR was studied using CST-PS (PIC) solver and multipacting band is predicted. Additional considerations were given to see the effects of the coupling ports and the coupler on the multipaction. We present the modified cavity design without multipaction at our operation accelerating voltage~1.2MV.

THP028

The Research on Spoke 0.40 Cavity

cavity, proton, linac, superconducting-cavity

959

P. Sha, H. Huang
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
W.M. Pan, X.Y. Zhang
IHEP, Beijing, People's Republic of China

Spoke superconducting cavity can be used in the low-energy section of the proton accelerator. It has many significant advantages: compact structure, high value of R/Q, etc. The Chinese ADS (Accelerator Driven System) project will adopt many spoke cavities with 3 different β values (0.12, 0.21, 0.40). Spoke040 cavities (β=0.40) are used to increase the proton energy from 34 MeV to 178 MeV. Now the physical design of spoke040 cavity has been finished, and the machining are going on right now. The vertical test would be held at the end of this year.

THP029

Simulation of Mechanical Resonances of SRF Cavities in Low Beam Current CW Operation

cavity, resonance, operation, cryomodule

962

N. Solyak, M.H. Awida, I.V. Gonin, T.N. Khabiboulline, Y.M. Pischalnikov, W. Schappert, V.P. Yakovlev
Fermilab, Batavia, USA

The low beam current for CW operation of the Project X requires cavities to be mechanically optimized to operate at a high loaded Q and thus, low bandwidth with higher sensitivity to microphonics. The essential source of microphonics detuning is fluctuations in the helium pressure df/dp. Last year’s several methods for reducing df/dp has been proposed. One of the other possible sources of RF frequency instability is mechanical resonances. The cavity could be driven out of operating frequency by the mechanical deformations due to vibrations caused by external factors. In this paper we present the COMSOL multiphysics algorithm developed for evaluation of operating frequency shift due to mechanical resonances in SC cavities. We discuss the results of simulations for 5-cell elliptical 650 MHz β=0.9 cavities. The comparison of COMSOL simulations and measurements of ILC type cavities in Horizontal Test Stand at Fermilab is presented.

THP031

Superconducting Test of the 56 MHz SRF Quarter Wave Resonator for RHIC

cavity, SRF, electron, resonance

969

Q. Wu, S.A. Belomestnykh, I. Ben-Zvi, G.T. McIntyre, R. Porqueddu, S.K. Seberg, T. Xin
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
A 56 MHz superconducting RF cavity will be the first quarter wave resonator (QWR) installed in a high energy storage ring. It is expected to boost the luminosity of the Relativistic Heavy Ion Collider by more than 60% after installation. In this paper, we discuss the cavity parameters and design features. We report the results from the first vertical test of this cavity at 4 K.

THP033

Study of Balloon Spoke Cavities

cavity, TRIUMF, operation, proton

972

Z.Y. Yao, R.E. Laxdal, B.S. Waraich, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
R. Edinger
PAVAC, Richmond, B.C., Canada

A balloon geometry has been proposed to suppress multipacting for single spoke resonators. The design may find a useful application for proton and ion accelerator projects. TRIUMF has completed initial RF, mechanical, and fabrication studies on this special geometry for both low (β=0.12) and medium (β=0.3) β geometries. The RF properties are comparable with that of traditional spoke cavities but with improved RF efficiency in addition to the reduced multipacting. The results of electro-magnetic and structural design studies comparing the balloon geometry with traditional spoke geometries will be presented. We will also present optimization studies of the mechanical design, such as decreasing df/dp by EM field compensation as well as discussing tuning strategies and fabrication techniques.

THP034

Multipacting Suppression in a Single Spoke Cavity

cavity, electron, resonance, operation

975

Z.Y. Yao, R.E. Laxdal, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
X.Y. Lu, K. Zhao
PKU, Beijing, People's Republic of China

Spoke cavities are good candidates for the low and medium β section of a high intensity proton or ion accelerator. For many high intensity accelerators, stability and reliability are the most important properties. Currently, one of the key issues of spoke cavity performance is multipacting, which may cause instability during operation. Multipacting in a spoke cavity has a troublesome characteristic as it presents a continual barrier over a wide gradient range, usually in the range of operation from 3MV/m to 15MV/m. A good surface processing can improve the secondary electron emission yield. However, the complex 3D structure makes it not easily achievable as with the elliptical cavity variants. Suppressing multipacting in the design stage is clearly advantageous. This paper will present a multipacting study based on the PKU-I spoke cavity. A systematic correlation between geometric parameters and multipacting behaviors is obtained. Based on this study a new geometry of single spoke cavity called the ‘balloon’ variant is proposed.

THP038

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

cavity, niobium, 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

THP039

Design of a Triple-Spoke Cavity as a Rebuncher for RIKEN RI-Beam Factory

cavity, factory, heavy-ion, acceleration

988

L. Lu
RIKEN, Saitama, Japan
O. Kamigaito, N. Sakamoto, K. Suda, K. Yamada
RIKEN Nishina Center, Wako, Japan

A superconducting triple-spoke cavity as a rebuncher for very heavy ion beams such as uranium at β=0.303 for RIKEN RI-beam factory is designed. The required total gap voltage is 3 MV. In this design, thick ribs (25 mm) are placed on the both ends of cavity so that the deformation caused by pressure of liquid helium is less than 0.5 mm. A copper test model with one spoke is designed to be fabricated using the same technique as that for Nb cavity. The detailed design will be presented.

THP040

3D MULTIPACTING STUDY FOR THE ROSSENDORF SRF GUN

electron, gun, SRF, cathode

991

E.T. Tulu, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A. Arnold
HZDR, Dresden, Germany

Funding: *This work is supported by Federal Ministry for Research and Education BMBF
Electron multipacting is still observed in the Rossendorf SRF gun which limits the cavity fields (accelerating gradient). To better understand this process, a three-cell 1.3 GHz elliptical-shape cavity with cathode was modeled in CST Studio Suite® 2013 at the University of Rostock. All parameters are provided by Helmholtz-Zentrum Dresden-Rossendorf. The multipacting simulations have been performed with CST Microwave Studio® (CST MWS) [1] and CST Particle Studio® (CST PS) which is suitable and powerful for 3D electromagnetic designs and provides the most advanced model of secondary emission. The radio frequency fields are calculated using the frequency domain solver of CST MWS, whereas the CST PS is used for particle tracking simulation [2]. The purpose of these numerical simulations is to better comprehend multipacting in the Rossendorf SRF gun and make a detailed analysis. The midterm goal is to find a new cavity shape, which might suppress the electron amplification so that the SRF Gun will be able to operate up to an accelerating gradient of 50 MV/m.
#eden.tulu@uni-rostock.de
[1] CST AG, Bad Nauheimer Str. 19, D-64289 Darmstadt, Germany
[2] F. Hamme, U. Becker and P. Hammes, Proc. of ICAP 2006, Chamonix, France

THP042

High Frequency SRF Cavity Study for Bunch Shortening in PEPX

cavity, HOM, SRF, FEL

998

L. Xiao, K.L.F. Bane, Y. Cai, X. Huang, C.-K. Ng, A. Novokhatski, L. Wang
SLAC, Menlo Park, California, USA

The proposed PEPX is a diffraction limited storage ring light source, or “ultimate storage ring (USR)”, which can be built in the PEP tunnel at SLAC. The 4.5GeV PEPX design based on the USR with a natural emittance about 10pm-rad can be used to drive a high-gain soft X-ray FEL. In order to achieve a desired high peak current over 300A for the FEL, the bunch length is reduced to 1ps from 10ps through a set of multi-cell SRF cavities working at 1.428GHz in CW mode, providing about 300MV RF gradient. In this paper, the 1.5GHz JLAB C100 cavity for the CEBAF upgrade and 1.3GHz Cornell ERL cavity are investigated for its application to PEPX-FEL. The simulation results show that the beam induced high order modes (HOM) in the C100 cavities will limit the threshold of the beam current for PEPX-FEL. And the same pass band modes (SPM) in the cavities are strongly trapped, and thus generate unacceptable beam power once they hit the beam resonances. Therefore, a 5-cell with a larger iris cavity design instead of the C100 7-cell design is proposed. Preliminary results on the rf parameters of the cavity, HOM damping and beam dynamics studies will be presented.

THP043

Design and Vertical Test of Double Quarter Wave Crab Cavity for LHC Luminosity Upgrade

cavity, cryogenics, pick-up, HOM

1002

B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, R. Calaga, C. Cullen, L.R. Hammons, J. Skaritka, S. Verdú-Andrés, Q. Wu
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. DOE, and supported by EU FP7 HiLumi LHC - Grant Agreement 284404.
A proof of principle Double Quarter Wave Crab Cavity (DQWCC) was designed and fabricated for the Large Hadron Collider (LHC) luminosity upgrade. Vertical cryogenic test has been done in Brookhaven National Lab (BNL). We report the test results of this design.

THP044

Compact Higher Order Mode Filter for Crab Cavities in the Large Hadron Collider

HOM, cavity, luminosity, cryomodule

1006

B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, S. Verdú-Andrés, Q. Wu
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
R. Calaga
CERN, Geneva, Switzerland

Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. DOE, and supported by EU FP7 HiLumi LHC - Grant Agreement 284404.
A double quarter wave crab cavity was designed for the Large Hadron Collider luminosity upgrade. Starting from the analytical calculation of simplified RLC circuit, a compact higher order mode filter is developed for this cavity. Finite element simulation results are presented. The design concept is generic and can easily be adapted to other cavities.

THP050

Development of Power Coupler for Superconducting Spoke Cavities for China ADS Proton Linac

cavity, vacuum, coupling, Windows

1024

X. Chen, T.M. Huang, H.Y. Lin, Q. Ma, F. Meng, W.M. Pan, Y.H. Peng
IHEP, Beijing, People's Republic of China

Abstract: The China-ADS proton linac adopts β=0.12 superconducting Spoke cavities. Each cavity is powered via a 325MHz coaxial power coupler. The coupler is to feed 6kW maximum power though it is designed to handle at 15kW .Two coupler sets have been made by IHEP so far, and a 10kW RF power in continuous travelling wave mode has passed through the coupler during high power test in late January 2013. An introduction of this coupler design and the room temperature test results are presented in this paper.

THP058

Update on the European XFEL RF Power Input Coupler

cryogenics, superconductivity, linac, electron

1047

D. Kostin, W.-D. Möller
DESY, Hamburg, Germany
W. Kaabi
LAL, Orsay, France

European XFEL project is being currently realized in Hamburg, Germany. The 1.5 km 17.5 GeV linear electron accelerator is based on the 1.3GHz 9-cell TESLA type SRF cavity. The RF power input coupler design for the E-XFEL is based on well known TTF3 coupler design, used in FLASH accelerator. Coupler design was adapted for the industrial production with some parameters optimisation revisited and simulations done. Results are presented and discussed.

THP059

HOM Coupler Design Adjustment for CW operation of the 1.3 GHz 9-cell TESLA Type SRF Cavity

HOM, dipole, cavity, operation

1051

D. Kostin, W.-D. Möller, J.K. Sekutowicz
DESY, Hamburg, Germany

One of the key features of a modern research facility is its versatility, ability to adjust for a multitude of the applications and user needs. A challenge for the coming European XFEL is to become a multipurpose laboratory with a broad applications spectrum. Primarily, the XFEL is a pulsed machine. Encompassing the CW mode would be a worthy addition. CW operation of the 1.3GHz 9-cell TESLA Type SRF Cavity was performed several times at DESY and other Labs successfully. One of the difficulties was a heat load of the High Order Mode (HOM) couplers. To amend this HOM coupler design adjustement is proposed, simulated and modelled. Results are presented and discussed.

THP060

High Power RF Coupler for ADS Accelerating Cavities

cavity, operation, linac, Windows

1055

S.V. Kutsaev, M.P. Kelly, B. Mustapha, J.A. Nolen, P.N. Ostroumov
ANL, Argonne, USA

Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
Accelerator driven systems (ADS) require a high-power CW proton accelerator with proton beam energy near 1 GeV. High-gradient superconducting TEM-cavities are a natural choice for the front end of linac. This paper presents the design of superconducting low-beta half wave resonator operating at 162 MHz frequency for ADS, as well as a new 75 kW power coupler that has been designed at Argonne National Laboratory. This coupler would permit operations with an accelerating voltage of 3.0 MV with a beam current of 25 mA. The coupler includes a cold RF window which keeps the antenna at low temperature and a variable bellows section to adjust the coupling factor. The importance of these features for reliable operation will be discussed in detail.

THP061

Developments of HOM Dampers for SuperKEKB Superconducting Cavity

cavity, HOM, operation, factory

1058

M. Nishiwaki, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, Y. Morita
KEK, Ibaraki, Japan

Eight superconducting accelerating cavities were stably operated under a high beam current and a large beam induced HOM power in KEKB electron ring. The HOM power of 16 kW at the beam current of 1.4A was absorbed in two ferrite dampers attached to each cavity. In SuperKEKB, that is the upgrade machine of KEKB, the design beam current is 2.60 A. The HOM power of higher than 40 kW is expected to be induced. To cope with the large HOM power, precise evaluations of HOM power loads including HOM dampers were carried out. Then, new ferrite dampers with reinforced water cooling were developed and high-power tested. On the other hand, the evaluation indicated that an additional HOM damper can absorb significant amount of HOM power. Additional damper is effective to reduce each ferrite damper load. In this report, we will describe the results of high power tests of the new ferrite dampers, studies for additional dampers, and an installation plan for SuperKEKB.

THP062

Optimisation of the 3-Stub Tuner for Matching the Diamond SCRF Cavities

cavity, operation, coupling, storage-ring

1061

S.A. Pande, C. Christou, P. Gu, M. Jensen
Diamond, Oxfordshire, United Kingdom

The Diamond Storage Ring cavities are aperture coupled resulting in a fixed external Q. This results in the cavities being matched under certain conditions depending on the loss per turn, the beam current and the accelerating voltage. Operationally, there are advantages to limiting the accelerating voltage to improve reliability and lifetime, which at high beam current results in a mismatch and high reflected power. To match the cavities under such non-optimum operating conditions we use 3-stub tuners in the waveguide feeds. It has been observed, that certain configurations of the 3-stub tuners can improve the match of the cavity, but this can result in strong heating of the waveguide in the cryostat. Numerical simulations of the cavity along with the coupling waveguide and 3-stub tuners have been carried out using CST Studio for different beam loading conditions to optimise the 3-stub tuners for acceptable match and heating. In this paper we present the results of our simulations and comparisons with measurements for operation with different beam currents and cavity voltages.

THP066

SARAF Phase-I HWR Coupler Cooling Design

operation, linac, cavity, proton

1073

J. Rodnizki, Y. Ben Aliz, I. Fishman, A. Grin, Z. Horvitz, B. Kaizer, L. Weissman
Soreq NRC, Yavne, Israel

The Soreq Applied Research Accelerator Facility (SARAF) design is based on a 40 MeV 5 mA light ions superconducting RF linac. Phase I of SARAF delivers up to 2 mA CW proton beam in an energy range of 1.5-4.5 MeV. The maximum beam power that we have reached is 4.5 kW. The warming of the SARAF linac RF couplers is currently the main limiting factor for reaching higher CW beam power. The coupler cooling configuration was optimized by increasing the cold window copper braid and adding a copper braid to the top end, using CST Multiphysics and ANSYS steady state and transient solvers. The study was conducted for the heat load generated by the surface currents of a matched 4 kW forward CW power, simulated by the CST MWS FD solver. Multipacting is a known potential heat source that overheats the coupler in the vicinity of the cold window. The coupler overheat phenomena was experimentally studied as a function of DC bias voltage, and it was found that a 900 V bias reduces significantly the heating rate. As a result we expect that the beam power can be significantly increased. The long overheat period implies that optimization of the cooling configuration is still needed.

THP068

New Design of HOM Coupler Using Coaxial-like Rounded Waveguide

HOM, cavity, damping, operation

1081

M. Sawamura
Japan Atomic Energy Agency (JAEA), Gamma-ray Non-Destructive Assay Research Group, Tokai-mura, Ibaraki-ken, Japan
R. Hajima, R. Nagai, N. Nishimori
JAEA, Ibaraki-ken, Japan

It is important to damp higher-order modes (HOMs) of superconducting accelerators especially for energy-recovery linacs of high current operation. Though various types of HOM couplers, beam line HOM dampers and waveguide HOM couplers have been developed, there are some problems such as inner conductor heating of output connector for HOM couplers and low packing factor for beam line HOM dampers. We propose new design of HOM coupler. This coupler consists of a coaxial line coupled with a cavity or a beam pipe and a rounded waveguide which cuts off the accelerating mode. The rounded waveguide is similar to a coaxial line and the inner conductor and outer conductor are connected with a plate which corresponds to waveguide side wall. This enables the inner connector cooled down efficiently through the outer conductor. The calculation results of MW-STUDIO will be presented.

THP077

Coaxial Blade Tuner for European XFEL 3.9 GHz cavities

cavity, linac, operation, cryomodule

1101

R. Paparella, M. Bertucci, A. Bosotti
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

The European XFEL linac injector features a third harmonic section jointly realized by INFN and DESY and hosting a 3.9 GHz 9-cell cavities cryomodule. The cold tuning system, developed by INFN for these cavities, is inspired by the coaxial Blade Tuner already qualified for ILC cavities. Design, fabrication and room temperature qualification of first tuner units produced are reviewed in this paper.

THP084

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

cavity, niobium, 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.

THP095

Error Analysis for Vertical Test Stand Cavity Measurements at Fermilab

cavity, detector, resonance, SRF

1148

O.S. Melnychuk
Fermilab, Batavia, USA

Overview of Vertical Test Stand (VTS) facility at Fermilab is presented. Uncertainty calculations for the measurements of quality factor and accelerating field are described Sources of uncertainties and assumptions on their correlations are reviewed. VTS hardware components with non-negligible instrumental errors are discussed. Relative contributions of individual sources to the total uncertainties are assessed. Stability of VTS test results with respect to potential mismeasurements of calibration coefficients and decay constant are studied.

FRIOC01

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

cavity, cryomodule, operation, niobium

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]