SRF2013 - List of Keywords (laser)

Paper	Title	Other Keywords	Page
MOIOB02	Towards a 100mA Superconducting RF Photoinjector for BERLinPro	cavity, cathode, emittance, SRF	42
	A. Neumann, W. Anders, A. Burrill, A. Jankowiak, T. Kamps, J. Knobloch, O. Kugeler, P. Lauinger, A.N. Matveenko, M. Schmeißer, J. Völker HZB, Berlin, Germany G. Ciovati, P. Kneisel JLAB, Newport News, Virginia, USA R. Nietubyć NCBJ, Świerk/Otwock, Poland S.G. Schubert, J. Smedley BNL, Upton, Long Island, New York, USA J.K. Sekutowicz DESY, Hamburg, Germany V. Volkov BINP SB RAS, Novosibirsk, Russia I. Will MBI, Berlin, Germany E.N. Zaplatin FZJ, Jülich, Germany
	For BERLinPro, a 100 mA CW-driven SRF energy recovery linac demonstrator facility, HZB needs to develop a photo-injector superconducting cavity which delivers a at least 1mmmr emittance beam at high average current. To address these challenges of producing a high peak brightness beam at high repetition rate, at first HZB tested a fully superconducting injector with a lead cathode,followed now by the design of a SC cavity allowing operation up to 4 mA using CW-modified TTF-III couplers and inserting a normal conducting high quantum efficiency cathode using the HZDR-style insert scheme. This talk will present the latest results and an overview of the measurements with the lead cathode cavity and will describe the design and optimization process, the first production results of the current design and an outlook to the further development steps towards the full power version. *T. Kamps et al., Proceedings of the 2nd International Particle Accelerator Conference, San Sebastián, Spain, 2011.
	Slides MOIOB02 [7.574 MB]

MOP009	A Summary of the Advanced Photon Source (APS) Short Pulse X-ray (SPX) R&D Accomplishments	cavity, cryomodule, LLRF, vacuum	92
	A. Nassiri, N.D. Arnold, T.G. Berenc, M. Borland, B. Brajuskovic, D.J. Bromberek, J. Carwardine, G. Decker, L. Emery, J.D. Fuerst, J.P. Holzbauer, D. Horan, J.A. Kaluzny, J.S. Kerby, F. Lenkszus, R.M. Lill, H. Ma, V. Sajaev, B.K. Stillwell, G.J. Waldschmidt, M. White, G. Wu, Y. Yang, A. Zholents ANL, Argonne, USA J.M. Byrd, L.R. Doolittle, G. Huang LBNL, Berkeley, California, USA P. Dhakal, J. Henry, J.D. Mammosser, J. Matalevich, R.A. Rimmer, H. Wang, K.M. Wilson JLAB, Newport News, Virginia, USA Z. Li, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357. The Advanced Photon Source Upgrade Project (APS-U) at Argonne will include generation of short-pulse x-rays based on Zholents’ [1] deflecting cavity scheme. We have chosen superconducting (SC) cavities in order to have a continuous train of crabbed bunches and flexibility of operating modes. Since early 2012, in collaboration with Jefferson National Laboratory, we have made significant progress prototyping and testing a number of single-cell deflecting cavities. We have designed, prototyped, and tested silicon carbide as damping material for higher-order-mode (HOM) dampers, which are broadband to handle the HOM power across the frequency spectrum produced by the APS beam. In collaboration with Lawrence Berkeley National Laboratory, we have developing a state-of-the-art timing and synchronization system for distributing stable rf signals over optical fiber capable of achieving tens of femtoseconds phase drift and jitter. Collaboration with the Advanced Computations Department at Stanford Linear Accelerator Center is looking into simulations of complex, multi- cavity geometries. This contribution provides a progress report on the current R&D status of the SPX project. [1] A. Zholents et al., NIM A 425, 385 (1999).

MOP020	Progress of the LUNEX5 Project	FEL, electron, undulator, operation	133
	P. Marchand, C. Benabderrahmane, L. Cassinari, M.-E. Couprie, J. Daillant, M. Diop, M.E. El Ajjouri, N. Hubert, M. Labat, R. Lopes, A. Loulergue, M. Louvet, O. Marcouillé, J.L. Marlats, C. Miron, P. Morin, A. Nadji, F. Ribeiro, P. Roy, K. Tavakoli SOLEIL, Gif-sur-Yvette, France S. Bielawski, C. Evain, E. Roussel, C. Szwaj PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France B. Carré, D. Garzella CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France N. Delerue LAL, Orsay, France G. Devanz, M. Luong CEA/DSM/IRFU, France A. Dubois, J. Lüning CCPMR, Paris, France G. Lambert, R. Lehe, A. Lifschitz, V. Malka, A. Rousse, C. Thaury LOA, Palaiseau, France
	LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. It comprises two types of accelerators connected to a single Free Electron Laser (FEL), enabling the most advanced seeding configurations : High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with cryogenic in-vacuum undulators. The 400 MeV Conventional Linear Accelerator (CLA) uses superconducting cavities, compatible with a future upgrade towards high repetition rate for investigating advanced FEL schemes. It will also enable multi-user operation by splitting part of the macropulse to different FEL lines. A 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA) will also be qualified in view of FEL applications, in the single spike or seeded regime. After the Conceptual Design Report, R&D has been launched on a cryo-ready 3 m long in-vacuum undulator, variable strong permanent magnet quadrupoles, Smith-Purcell and electro-optics diagnostics. A test experiment is also under preparation for validating the computed beam transport from the LWFA.

MOP024	Novel SRF Gun Design	gun, cathode, cavity, SRF	145
	F. Marhauser Muons, Inc, Illinois, USA K.H. Lee, Z. Li SLAC, Menlo Park, California, USA
	Funding: Work supported under U.S. DOE Grant Application Number 98802B12-I A high brightness superconducting radio frequency (SRF) photoinjector gun cavity has been developed to a level ready for construction. The design aims to prevent operational limitations encountered with existing concepts.

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

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

TUP008	Models of the Magnetic Field Enhancement at Pits	cavity, SRF, experiment, radio-frequency	433
	T. Kubo KEK, Ibaraki, Japan
	A simple model of the magnetic field enhancement at pits on the surface of superconducting accelerating cavity is proposed. The model consists of a two-dimensional pit with a slope angle, depth, width, and radius of round edge. An analytical formula that describes the magnetic field enhancement factor of the model is derived. The formula is given as a function of a slope angle and a ratio of half a width to a round-edge radius. Using the formula, the field at which vortices start to penetrate can be evaluated for a given geometry of pit. Takayuki Kubo, arXiv:1307.5943 [physics.acc-ph](Submitted on 23 Jul 2013)

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

TUP019	Probing Hot Spot and Cold Spot of SRF Cavities with Tunneling and Raman Spectroscopies	superconductivity, SRF, cavity, electron	466
	C. Cao Illinois Institute of Technology, Chicago, IL, USA G. Ciovati JLAB, Newport News, Virginia, USA L.D. Cooley, A. Grassellino Fermilab, Batavia, USA N. Groll, Th. Proslier ANL, Argonne, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Point contact tunneling and Raman spectroscopies are presented on high purity Nb samples, including pieces from hot and col spot regions of tested SRF cavities and Nb coupons subject to similar treatment. High quality tunneling spectra were observed on cold spots, revealing the bulk Nb gap, indicating minimal surface contamination. Hot spots exhibit high smearing suggestive of pair breaking along with generally lower superconducting gap. In addition, pronounced zero bias conductance peaks were frequently observed indicative of spin-flip tunneling and thus magnetic impurities in the oxide layer. Optical microscopy reveals higher density of surface blemishes on hot spots. Raman spectra inside those blemishes show clear difference from surrounding areas, exhibiting enhanced intensity peaks identified as either amorphous carbon, hydrocarbons or the ordered NbC phase. The presence of surface NbC is consistent with TEM studies, and these inclusions exhibit enhanced second order phonon response. Such regions with high concentrations of impurities are expected to suppress the local superconductivity and may explain the formation of hot spots.

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

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

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

Paper

Title

Other Keywords

Page

MOIOB02

Towards a 100mA Superconducting RF Photoinjector for BERLinPro

cavity, cathode, emittance, SRF

42

A. Neumann, W. Anders, A. Burrill, A. Jankowiak, T. Kamps, J. Knobloch, O. Kugeler, P. Lauinger, A.N. Matveenko, M. Schmeißer, J. Völker
HZB, Berlin, Germany
G. Ciovati, P. Kneisel
JLAB, Newport News, Virginia, USA
R. Nietubyć
NCBJ, Świerk/Otwock, Poland
S.G. Schubert, J. Smedley
BNL, Upton, Long Island, New York, USA
J.K. Sekutowicz
DESY, Hamburg, Germany
V. Volkov
BINP SB RAS, Novosibirsk, Russia
I. Will
MBI, Berlin, Germany
E.N. Zaplatin
FZJ, Jülich, Germany

For BERLinPro, a 100 mA CW-driven SRF energy recovery linac demonstrator facility, HZB needs to develop a photo-injector superconducting cavity which delivers a at least 1mm*mr emittance beam at high average current. To address these challenges of producing a high peak brightness beam at high repetition rate, at first HZB tested a fully superconducting injector with a lead cathode*,followed now by the design of a SC cavity allowing operation up to 4 mA using CW-modified TTF-III couplers and inserting a normal conducting high quantum efficiency cathode using the HZDR-style insert scheme. This talk will present the latest results and an overview of the measurements with the lead cathode cavity and will describe the design and optimization process, the first production results of the current design and an outlook to the further development steps towards the full power version.
*T. Kamps et al., Proceedings of the 2nd International Particle Accelerator Conference, San Sebastián, Spain, 2011.

Slides MOIOB02 [7.574 MB]

MOP009

A Summary of the Advanced Photon Source (APS) Short Pulse X-ray (SPX) R&D Accomplishments

cavity, cryomodule, LLRF, vacuum

92

A. Nassiri, N.D. Arnold, T.G. Berenc, M. Borland, B. Brajuskovic, D.J. Bromberek, J. Carwardine, G. Decker, L. Emery, J.D. Fuerst, J.P. Holzbauer, D. Horan, J.A. Kaluzny, J.S. Kerby, F. Lenkszus, R.M. Lill, H. Ma, V. Sajaev, B.K. Stillwell, G.J. Waldschmidt, M. White, G. Wu, Y. Yang, A. Zholents
ANL, Argonne, USA
J.M. Byrd, L.R. Doolittle, G. Huang
LBNL, Berkeley, California, USA
P. Dhakal, J. Henry, J.D. Mammosser, J. Matalevich, R.A. Rimmer, H. Wang, K.M. Wilson
JLAB, Newport News, Virginia, USA
Z. Li, L. Xiao
SLAC, Menlo Park, California, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06H11357.
The Advanced Photon Source Upgrade Project (APS-U) at Argonne will include generation of short-pulse x-rays based on Zholents’ [1] deflecting cavity scheme. We have chosen superconducting (SC) cavities in order to have a continuous train of crabbed bunches and flexibility of operating modes. Since early 2012, in collaboration with Jefferson National Laboratory, we have made significant progress prototyping and testing a number of single-cell deflecting cavities. We have designed, prototyped, and tested silicon carbide as damping material for higher-order-mode (HOM) dampers, which are broadband to handle the HOM power across the frequency spectrum produced by the APS beam. In collaboration with Lawrence Berkeley National Laboratory, we have developing a state-of-the-art timing and synchronization system for distributing stable rf signals over optical fiber capable of achieving tens of femtoseconds phase drift and jitter. Collaboration with the Advanced Computations Department at Stanford Linear Accelerator Center is looking into simulations of complex, multi- cavity geometries. This contribution provides a progress report on the current R&D status of the SPX project.
[1] A. Zholents et al., NIM A 425, 385 (1999).

MOP020

Progress of the LUNEX5 Project

FEL, electron, undulator, operation

133

P. Marchand, C. Benabderrahmane, L. Cassinari, M.-E. Couprie, J. Daillant, M. Diop, M.E. El Ajjouri, N. Hubert, M. Labat, R. Lopes, A. Loulergue, M. Louvet, O. Marcouillé, J.L. Marlats, C. Miron, P. Morin, A. Nadji, F. Ribeiro, P. Roy, K. Tavakoli
SOLEIL, Gif-sur-Yvette, France
S. Bielawski, C. Evain, E. Roussel, C. Szwaj
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
B. Carré, D. Garzella
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
N. Delerue
LAL, Orsay, France
G. Devanz, M. Luong
CEA/DSM/IRFU, France
A. Dubois, J. Lüning
CCPMR, Paris, France
G. Lambert, R. Lehe, A. Lifschitz, V. Malka, A. Rousse, C. Thaury
LOA, Palaiseau, France

LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. It comprises two types of accelerators connected to a single Free Electron Laser (FEL), enabling the most advanced seeding configurations : High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with cryogenic in-vacuum undulators. The 400 MeV Conventional Linear Accelerator (CLA) uses superconducting cavities, compatible with a future upgrade towards high repetition rate for investigating advanced FEL schemes. It will also enable multi-user operation by splitting part of the macropulse to different FEL lines. A 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA) will also be qualified in view of FEL applications, in the single spike or seeded regime. After the Conceptual Design Report, R&D has been launched on a cryo-ready 3 m long in-vacuum undulator, variable strong permanent magnet quadrupoles, Smith-Purcell and electro-optics diagnostics. A test experiment is also under preparation for validating the computed beam transport from the LWFA.

MOP024

Novel SRF Gun Design

gun, cathode, cavity, SRF

145

F. Marhauser
Muons, Inc, Illinois, USA
K.H. Lee, Z. Li
SLAC, Menlo Park, California, USA

Funding: Work supported under U.S. DOE Grant Application Number 98802B12-I
A high brightness superconducting radio frequency (SRF) photoinjector gun cavity has been developed to a level ready for construction. The design aims to prevent operational limitations encountered with existing concepts.

MOP036

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

cavity, vacuum, niobium, experiment

186

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

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

TUIOA05

New Insights Into Quench Caused by Surface Pits in SRF Cavities

cavity, niobium, SRF, feedback

378

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

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

Slides TUIOA05 [3.101 MB]

TUP008

Models of the Magnetic Field Enhancement at Pits

cavity, SRF, experiment, radio-frequency

433

T. Kubo
KEK, Ibaraki, Japan

A simple model of the magnetic field enhancement at pits on the surface of superconducting accelerating cavity is proposed. The model consists of a two-dimensional pit with a slope angle, depth, width, and radius of round edge. An analytical formula that describes the magnetic field enhancement factor of the model is derived. The formula is given as a function of a slope angle and a ratio of half a width to a round-edge radius. Using the formula, the field at which vortices start to penetrate can be evaluated for a given geometry of pit.
Takayuki Kubo, arXiv:1307.5943 [physics.acc-ph](Submitted on 23 Jul 2013)

TUP014

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

niobium, cavity, cryogenics, vacuum

447

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

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

TUP019

Probing Hot Spot and Cold Spot of SRF Cavities with Tunneling and Raman Spectroscopies

superconductivity, SRF, cavity, electron

466

C. Cao
Illinois Institute of Technology, Chicago, IL, USA
G. Ciovati
JLAB, Newport News, Virginia, USA
L.D. Cooley, A. Grassellino
Fermilab, Batavia, USA
N. Groll, Th. Proslier
ANL, Argonne, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Point contact tunneling and Raman spectroscopies are presented on high purity Nb samples, including pieces from hot and col spot regions of tested SRF cavities and Nb coupons subject to similar treatment. High quality tunneling spectra were observed on cold spots, revealing the bulk Nb gap, indicating minimal surface contamination. Hot spots exhibit high smearing suggestive of pair breaking along with generally lower superconducting gap. In addition, pronounced zero bias conductance peaks were frequently observed indicative of spin-flip tunneling and thus magnetic impurities in the oxide layer. Optical microscopy reveals higher density of surface blemishes on hot spots. Raman spectra inside those blemishes show clear difference from surrounding areas, exhibiting enhanced intensity peaks identified as either amorphous carbon, hydrocarbons or the ordered NbC phase. The presence of surface NbC is consistent with TEM studies, and these inclusions exhibit enhanced second order phonon response. Such regions with high concentrations of impurities are expected to suppress the local superconductivity and may explain the formation of hot spots.

TUP068

Laser Polishing of Niobium for SRF Applications

niobium, experiment, SRF, simulation

593

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

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

Poster TUP068 [1.011 MB]

TUP085

Study of NbTi Welded Parts

niobium, cavity, plasma, linac

659

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

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

WEIOA04

Nb3Sn for SRF Application

niobium, cavity, SRF, vacuum

773

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

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

Slides WEIOA04 [3.854 MB]