SRF2015 - List of Authors (Gruber, T.)

Paper	Title	Page
MOBA08	Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0	55
	M. Liepe, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As part of a multi-laboratory research initiative on high Q0 niobium cavities for LCLS-II and other future CW SRF accelerators, Cornell has conducted an extensive research program during the last two years on impurity-doping of niobium cavities and related material characterization. Here we give an overview of these activities, and present results from single-cell studies, from vertical performance testing of nitrogen-doped nine-cell cavities, and from cryomodule testing of nitrogen-doped nine-cell cavities.
	Slides MOBA08 [8.983 MB]
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MOPB033	LCLS-II SRF Cavity Processing Protocol Development and Baseline Cavity Performance Demonstration	159
	M. Liepe, P. Bishop, H. Conklin, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, G. Kulina, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Checchin, A.C. Crawford, A. Grassellino, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, A. Romanenko, A.M. Rowe, D.A. Sergatskov, W.M. Soyars, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, A.D. Palczewski, C.E. Reece JLab, Newport News, Virginia, USA M.C. Ross SLAC, Menlo Park, California, USA
	Funding: Work supported, in part, by the US DOE and the LCLS-II Project under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-76SF00515. The ”Linac Coherent Light Source-II” Project will construct a 4 GeV CW superconducting RF linac in the first kilometer of the existing SLAC linac tunnel. The baseline design calls for 280 1.3 GHz nine-cell cavities with an average intrinsic quality factor Q0 of 2.7·10¹⁰ at 2K and 16 MV/m accelerating gradient. The LCLS-II high Q0 cavity treatment protocol utilizes the reduction in BCS surface resistance by nitrogen doping of the RF surface layer, which was discovered originally at FNAL. Cornell University, FNAL, and TJNAF conducted a joint high Q0 R&D program with the goal of (a) exploring the robustness of the N-doping technique and establishing the LCLS-II cavity high Q0 processing protocol suitable for production use, and (b) demonstrating that this process can reliably achieve LCLS-II cavity specification in a production acceptance testing setting. In this paper we describe the LCLS-II cavity protocol and analyze combined cavity performance data from both vertical and horizontal testing at the three partner labs, which clearly shows that LCLS-II specifications were met, and thus demonstrates readiness for LCLS-II cavity production.
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MOPB042	Fundamental Studies on Doped SRF Cavities	187
	D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.
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MOPB084	Performance of Nitrogen-Doped 9-Cell SRF Cavities in Vertical Tests at Cornell University	328
	G.M. Ge, R.G. Eichhorn, B. Elmore, F. Furuta, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, J. Sears, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University treated five LCLS-II 9-cell cavities by nitrogen-doping recipe. In this paper, we reported the performance of these 9-cell cavities. In the treatments, the nitrogen recipes are slightly different. The cavities have been firstly doped under high nitrogen pressure; after the vertical tests some of the cavities has been reset the surface and re-doped under light nitrogen pressure. The detail of the cavity preparation and test results will be shown. The comparison of the different recipes will be discussed.
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MOPB093	Vertical Electropolishing Studies at Cornell	364
	F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA H. Hayano, T. Saeki KEK, Ibaraki, Japan Y.I. Ida, K.N. Nii MGH, Hyogo-ken, Japan
	Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.
	Poster MOPB093 [4.364 MB]
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TUBA04	Nb3Sn Cavities: Material Characterization and Coating Process Optimization	501
	D.L. Hall, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, S. Posen, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Th. Proslier ANL, Argonne, Illinois, USA
	Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296) Recent progress on vapour diffusion coated Nb3Sn SRF cavities makes this material a very promising alternative for CW medium field SRF applications. In this paper we report on several systematic studies to determine the sources currently limiting the performance of Nb3Sn cavities to determine improved coating parameters to overcome these limitations. These include a detailed study of the sensitivity of Nb3Sn to trapped ambient magnetic flux, a first measurement of the field dependence of the energy gap in Nb3Sn and detailed measurements of the stoichiometry of the obtained Nb3Sn coatings with synchrotron x-ray diffraction and STEM. Initial results from a study on the impact of the coating process parameters on energy gap, Q-slope, and residual resistance, show clear dependencies, and thus directions for process optimization.
	Slides TUBA04 [3.872 MB]
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TUPB030	Recent Results from the Cornell Sample Host Cavity	626
	J.T. Maniscalco, B. Clasby, T. Gruber, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE/NSF Many novel materials are under investigation for the future of superconducting radio-frequency accelerators (SRF). In particular, thin-film materials such as Nb3Sn, NbN, SIS multilayers, and also thin-film niobium on copper, may offer improvements in cost efficiency and RF performance over the standard niobium cavities. To avoid the difficulties of depositing thin films on full cavities, Cornell has developed a TE-mode sample host cavity which allows for RF measurements of large, flat samples at fields up to and over 100 mT. We present recent performance results from the cavity, reaching record high fields and quality factor using a niobium calibration plate. We also discuss plans for future collaborations.
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TUPB044	High Quality Factor Studies in SRF Nb3Sn Cavities	661
	D.L. Hall, B. Clasby, H. Conklin, R.G. Eichhorn, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638 A significant advantage of Nb3Sn coated on niobium over conventional bulk niobium is the substantial reduction in the BCS losses at equal temperatures of the former relative to the latter. The quality factor of a 1.3 GHz Nb3Sn cavity is thus almost entirely dictated by the residual resistance at temperatures at and below 4.2 K, which, if minimised, offers the ability to operate the cavity in liquid helium at atmospheric pressure with quality factors exceeding 4·10¹⁰. In this paper we look at the impact of the cooldown procedure – which is intrinsically linked to the effect of spatial and temporal gradients – and the impact of external ambient magnetic fields on the performance of a Nb3Sn cavity.
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TUPB045	Surface Analysis and Material Property Studies of Nb3Sn on Niobium for Use in SRF Cavities	665
	D.L. Hall, H. Conklin, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Th. Proslier ANL, Argonne, Illinois, USA
	Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296) Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing.
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THBA05	Higher Order Mode Absorbers for High Current SRF Applications	1036
	R.G. Eichhorn, J.V. Conway, T. Gruber, Y. He, G.H. Hoffstaetter, Y. Li, M. Liepe, T.I. O'Connell, P. Quigley, J. Sears, V.D. Shemelin, E.N. Smith, M. Tigner Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Efficient damping of the higher-order modes (HOMs) of the superconducting cavities is essential for any high current operation. The talk will provide an overview on the latest advances of HOM absorber development for high intensity SRF applications. As the ideal absorber does not exist, the different conceptual approaches will be presented and the associated issues are outlined. Design examples from various labs will be given that help explain the issues and resolutions. Some focus will be given to the Cornell HOM beamline absorber that was design for high current, short bunch operation with up to 400 W heating. The design will be reviewed and testing results will be reported.
	Slides THBA05 [4.022 MB]
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Paper

Title

Page

Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0

55

M. Liepe, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

As part of a multi-laboratory research initiative on high Q0 niobium cavities for LCLS-II and other future CW SRF accelerators, Cornell has conducted an extensive research program during the last two years on impurity-doping of niobium cavities and related material characterization. Here we give an overview of these activities, and present results from single-cell studies, from vertical performance testing of nitrogen-doped nine-cell cavities, and from cryomodule testing of nitrogen-doped nine-cell cavities.

Slides MOBA08 [8.983 MB]

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MOPB033

LCLS-II SRF Cavity Processing Protocol Development and Baseline Cavity Performance Demonstration

159

M. Liepe, P. Bishop, H. Conklin, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, G. Kulina, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Checchin, A.C. Crawford, A. Grassellino, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, A. Romanenko, A.M. Rowe, D.A. Sergatskov, W.M. Soyars, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA
E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA
M.C. Ross
SLAC, Menlo Park, California, USA

Funding: Work supported, in part, by the US DOE and the LCLS-II Project under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-76SF00515.
The ”Linac Coherent Light Source-II” Project will construct a 4 GeV CW superconducting RF linac in the first kilometer of the existing SLAC linac tunnel. The baseline design calls for 280 1.3 GHz nine-cell cavities with an average intrinsic quality factor Q0 of 2.7·10¹⁰ at 2K and 16 MV/m accelerating gradient. The LCLS-II high Q0 cavity treatment protocol utilizes the reduction in BCS surface resistance by nitrogen doping of the RF surface layer, which was discovered originally at FNAL. Cornell University, FNAL, and TJNAF conducted a joint high Q0 R&D program with the goal of (a) exploring the robustness of the N-doping technique and establishing the LCLS-II cavity high Q0 processing protocol suitable for production use, and (b) demonstrating that this process can reliably achieve LCLS-II cavity specification in a production acceptance testing setting. In this paper we describe the LCLS-II cavity protocol and analyze combined cavity performance data from both vertical and horizontal testing at the three partner labs, which clearly shows that LCLS-II specifications were met, and thus demonstrates readiness for LCLS-II cavity production.

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MOPB042

Fundamental Studies on Doped SRF Cavities

187

D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF
Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.

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MOPB084

Performance of Nitrogen-Doped 9-Cell SRF Cavities in Vertical Tests at Cornell University

328

G.M. Ge, R.G. Eichhorn, B. Elmore, F. Furuta, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, J. Sears, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell University treated five LCLS-II 9-cell cavities by nitrogen-doping recipe. In this paper, we reported the performance of these 9-cell cavities. In the treatments, the nitrogen recipes are slightly different. The cavities have been firstly doped under high nitrogen pressure; after the vertical tests some of the cavities has been reset the surface and re-doped under light nitrogen pressure. The detail of the cavity preparation and test results will be shown. The comparison of the different recipes will be discussed.

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MOPB093

Vertical Electropolishing Studies at Cornell

364

F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
Y.I. Ida, K.N. Nii
MGH, Hyogo-ken, Japan

Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.

Poster MOPB093 [4.364 MB]

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TUBA04

Nb3Sn Cavities: Material Characterization and Coating Process Optimization

501

D.L. Hall, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, S. Posen, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296)
Recent progress on vapour diffusion coated Nb3Sn SRF cavities makes this material a very promising alternative for CW medium field SRF applications. In this paper we report on several systematic studies to determine the sources currently limiting the performance of Nb3Sn cavities to determine improved coating parameters to overcome these limitations. These include a detailed study of the sensitivity of Nb3Sn to trapped ambient magnetic flux, a first measurement of the field dependence of the energy gap in Nb3Sn and detailed measurements of the stoichiometry of the obtained Nb3Sn coatings with synchrotron x-ray diffraction and STEM. Initial results from a study on the impact of the coating process parameters on energy gap, Q-slope, and residual resistance, show clear dependencies, and thus directions for process optimization.

Slides TUBA04 [3.872 MB]

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TUPB030

Recent Results from the Cornell Sample Host Cavity

626

J.T. Maniscalco, B. Clasby, T. Gruber, D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: DOE/NSF
Many novel materials are under investigation for the future of superconducting radio-frequency accelerators (SRF). In particular, thin-film materials such as Nb3Sn, NbN, SIS multilayers, and also thin-film niobium on copper, may offer improvements in cost efficiency and RF performance over the standard niobium cavities. To avoid the difficulties of depositing thin films on full cavities, Cornell has developed a TE-mode sample host cavity which allows for RF measurements of large, flat samples at fields up to and over 100 mT. We present recent performance results from the cavity, reaching record high fields and quality factor using a niobium calibration plate. We also discuss plans for future collaborations.

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TUPB044

High Quality Factor Studies in SRF Nb3Sn Cavities

661

D.L. Hall, B. Clasby, H. Conklin, R.G. Eichhorn, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638
A significant advantage of Nb3Sn coated on niobium over conventional bulk niobium is the substantial reduction in the BCS losses at equal temperatures of the former relative to the latter. The quality factor of a 1.3 GHz Nb3Sn cavity is thus almost entirely dictated by the residual resistance at temperatures at and below 4.2 K, which, if minimised, offers the ability to operate the cavity in liquid helium at atmospheric pressure with quality factors exceeding 4·10¹⁰. In this paper we look at the impact of the cooldown procedure – which is intrinsically linked to the effect of spatial and temporal gradients – and the impact of external ambient magnetic fields on the performance of a Nb3Sn cavity.

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TUPB045

Surface Analysis and Material Property Studies of Nb3Sn on Niobium for Use in SRF Cavities

665

D.L. Hall, H. Conklin, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296)
Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing.

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THBA05

Higher Order Mode Absorbers for High Current SRF Applications

1036

R.G. Eichhorn, J.V. Conway, T. Gruber, Y. He, G.H. Hoffstaetter, Y. Li, M. Liepe, T.I. O'Connell, P. Quigley, J. Sears, V.D. Shemelin, E.N. Smith, M. Tigner
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Efficient damping of the higher-order modes (HOMs) of the superconducting cavities is essential for any high current operation. The talk will provide an overview on the latest advances of HOM absorber development for high intensity SRF applications. As the ideal absorber does not exist, the different conceptual approaches will be presented and the associated issues are outlined. Design examples from various labs will be given that help explain the issues and resolutions. Some focus will be given to the Cornell HOM beamline absorber that was design for high current, short bunch operation with up to 400 W heating. The design will be reviewed and testing results will be reported.

Slides THBA05 [4.022 MB]

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