LINAC2016 - List of Authors (Liepe, M.)

Paper	Title	Page
MOPRC027	Surface Roughness Effect on the Performance of Nb3Sn Cavities	129
SPWR032	use link to see paper's listing under its alternate paper code
	R.D. Porter, D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE award DE-SC0008431 Surface roughness of current Niobium-3 Tin (Nb3Sn) superconducting radio-frequency (SRF) accelerator cavities can cause enhancement of the surface magnetic field. This enhancement can push the surface magnetic field beyond the critical field, which, if it occurs over a large enough area, can cause the cavity to quench. This paper presents simulations of the surface magnetic field enhancements in SRF cavities caused by the surface roughness of current Cornell Nb3Sn cavities, which have achieved record efficiency. Simple, smooth cavity geometry is defined and surface magnetic fields calculated using SLANS2. The cavity geometry is modified with a small rough region for which the geometry is determined from AFM scans of a Nb3Sn coated sample and the surface fields are calculated again. The calculated surface fields of the smooth and rough cavities are compared to determine the extent of the field enhancement, the area over which the enhancement is significant, and which surface features cause large field enhancement. We find that 1% of the surface analyzed has fields enhance by more than 45%. On average the Q-factor is increased by (3.8 ± 1.0) \%.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC027
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MOPLR047	Advanced Vertical Electro-Polishing studies at Cornell with Faraday	233
	F. Furuta, M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, 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
	Cornell's SRF group and Faraday Technology Inc. have started collaborations on two phase-II SBIR projects. Both projects are aiming for the development of advanced Vertical Electro-Polishing (VEP) for Nb SRF cavities, such as HF free or acid free VEP protocols. These could be eco-friendlier alternatives for the standard, HF-based EP electrolyte used, and could bring new breakthrough performance for Nb SRF cavities. Here we give a status update and report first results from these two projects.
	Poster MOPLR047 [2.852 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR047
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TUOP02	CBETA: The Cornell/BNL 4-Turn ERL with FFAG Return Arcs for eRHIC Prototyping	384
TUPLR002	use link to see paper's listing under its alternate paper code
	G.H. Hoffstaetter, J. Barley, A.C. Bartnik, I.V. Bazarov, J. Dobbins, B.M. Dunham, R.G. Eichhorn, R.E. Gallagher, C.M. Gulliford, Y. Li, M. Liepe, W. Lou, C.E. Mayes, J.R. Patterson, D.M. Sabol, E.N. Smith, K.W. Smolenski Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I. Ben-Zvi, J.S. Berg, S.J. Brooks, G.J. Mahler, F. Méot, M.G. Minty, S. Peggs, V. Ptitsyn, T. Roser, D. Trbojevic, N. Tsoupas, J.E. Tuozzolo, H. Witte BNL, Upton, Long Island, New York, USA D. Douglas JLab, Newport News, Virginia, USA
	Cornell University has prototyped technology essential for any high brightness electron ERL. This includes a DC gun and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current CW cryomodule, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams, e.g. slid measurements for 6-D phase-space densities, a fast wire scanner for beam profiles, and beam loos diagnostics. All these are now available to equip a one-cryomodule ERL, and laboratory space has been cleared out and is radiation shielded to install this ERL at Cornell. BNL has designed a multi-turn ERL for eRHIC, where beam is transported more than 20 times around the RHIC tunnel. The number of transport lines is minimized by using two non-scaling (NS) FFAG arcs. A collaboration between BNL and Cornell has been formed to investigate the new NS-FFAG optics and the multi-turn eRHIC ERL design by building a 4-turn, one-cryomodule ERL at Cornell. It has a NS-FFAG return loop built with permanent magnets and is meant to accelerate 40mA beam to 200MeV.
	Slides TUOP02 [7.848 MB]
	Poster TUOP02 [13.981 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP02
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TUOP07	High Performance Next-Generation Nb3Sn Cavities for Future High Efficiency SRF Linacs	398
TUPRC031	use link to see paper's listing under its alternate paper code
	D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE A 1.3 GHz ILC-shape single-cell Nb3Sn cavity fabricated at Cornell has shown record performance, exceeding the cryogenic efficiency of niobium cavities at the gradients and quality factors demanded by some contemporary accelerator designs. An optimisation of the coating process has resulted in more cavities of the same design that achieve similar performance, proving the reproducibility of the method. In this paper, we discuss the current limitations on the peak accelerating gradients achieved by these cavities. In particular, high-pulsed-power RF testing, and thermometry mapping of the cavity during CW operation, are used to draw conclusions regarding the nature of the quench limitation. In light of these promising results, the feasibility and utility of applying the current state of the technology to a real-life application is discussed.
	Slides TUOP07 [1.506 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP07
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TUPRC025	Low Temperature Nitrogen Baking of a Q0 SRF Cavities	472
	P.N. Koufalis, F. Furuta, M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Nitrogen-doping has led to an unprecedented increase in the intrinsic quality factor of bulk-niobium superconducting RF cavities. So far, high temperature baking in a nitrogen atmosphere is used almost exclusively to dope cavities. Recently, we have set focus on low temperature baking to produce similar performance increases and we present those results here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPRC025
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPLR010	Measurements and Analysis of Cavity Microphonics and Frequency Control in the Cornell ERL Main Linac Prototype Cryomodule	488
	M. Ge, N. Banerjee, J. Dobbins, R.G. Eichhorn, F. Furuta, G.H. Hoffstaetter, M. Liepe, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The Cornell Main Linac cryomodule (MLC) is a key component in the CBETA project. The SRF cavities with high loaded-Q in the MLC are very sensitive to microphonics from mechanical vibrations. Poor frequency stability of the cavities would dramatically increase the input RF power required to maintain stable accelerating fields in the SRF cavities. In this paper, we present detailed results from microphonics measurement for the cavities in the MLC, discuss dominant vibration sources, and show vibration damping results. The current microphonics level meets the CBETA requirement of a 36MeV energy gain without applying fast tuner compensation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR010
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TUPLR011	Performance of the Novel Cornell ERL Main Linac Prototype Cryomodule	492
	F. Furuta, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, 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
	The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based X-ray light source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Cavities have achieved the specification values of 16.2MV/m with high-Q of 2.0·10¹⁰ in 1.8K in continuous wave (CW) mode. During initial MLC cavity testing, we encountered some field emission, reducing Q and lowering quench field. To overcome field emission and find optimal cool-down parameters, RF processing and thermal cycles with different cool-down conditions has been done. Here we report on these studies and present final results from the MLC cavity performance.
	Poster TUPLR011 [2.389 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR011
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TUPLR012	HOM Measurements for Cornell's ERL Main Linac Cryomodule	496
	F. Furuta, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The main linac cryomodule (MLC) for a future energy-recovery linac (ERL) based X-ray source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. All HOMs in MLC have been scanned in 1.8K. The results show effective damping of HOMs, and also agree well with simulation results and the previous HOM scan results on one 7-cell cavity prototype test cryomodule. Here we present detailed results from these HOM studies.
	Poster TUPLR012 [2.773 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR012
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TUPLR025	Optimal Nitrogen Doping Level to Reach High Q0	523
	D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF and US DOE New continuous wave (CW) accelerators such as LCLS-II at SLAC require many SRF cavities operating in the medium field region at unprecedented high Q. In order to achieve this demanding goal, nitrogen-doping of the SRF cavities will be used. Nitrogen-doping has been shown to affect the BCS resistance both by a lowering of Rbcs at low fields and by the introduction of an anti-Q slope which enables the Q to continue increasing as the RF field is increased. The exact strength of this anti-Q slope is heavily dependent on the doping recipe and specifically the mean free path of the RF penetration layer of the doped cavities. In addition to its effect on Rbcs, the mean free path affects the amount of residual resistance obtained due to trapped magnetic flux. We have analyzed nine cavities prepared with different levels of nitrogen-doping to understand how BCS and residual resistance are affected by changes in the mean free path. Here we present a model based on these experimental results to predict the optimal doping level to reach the maximum Q at 16 MV/m based on the ambient magnetic field conditions. We find that if the cavities can be cooled with small amounts of trapped flux, moderate nitrogen-doping is better, while if they will have large amounts of trapped flux, lighter dopings should be used.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR025
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRC015	Cool-Down Performance of the Cornell ERL Cryomodules	802
	R.G. Eichhorn, F. Furuta, M. Ge, G.H. Hoffstaetter, M. Liepe, S.R. Markham, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich, D. Widger Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	In the framework of the ERL prototyping, Cornell University has built two cryomodules, one injector module and one prototype Main Linac Cryomodule (MLC). In 2015, the MLC was successfully cooled down for the first time. We will report details on the cool-down as well as cycle tests we did in order to achieve slow and fast cool-down of the cavities. We will also report on the improvement we made on the injector cryomodule which also included a modification of the heat exchanger can that allows now a more controlled cool-down, too.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPRC015
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

MOPRC027

Surface Roughness Effect on the Performance of Nb3Sn Cavities

129

SPWR032

use link to see paper's listing under its alternate paper code

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

Funding: DOE award DE-SC0008431
Surface roughness of current Niobium-3 Tin (Nb3Sn) superconducting radio-frequency (SRF) accelerator cavities can cause enhancement of the surface magnetic field. This enhancement can push the surface magnetic field beyond the critical field, which, if it occurs over a large enough area, can cause the cavity to quench. This paper presents simulations of the surface magnetic field enhancements in SRF cavities caused by the surface roughness of current Cornell Nb3Sn cavities, which have achieved record efficiency. Simple, smooth cavity geometry is defined and surface magnetic fields calculated using SLANS2. The cavity geometry is modified with a small rough region for which the geometry is determined from AFM scans of a Nb3Sn coated sample and the surface fields are calculated again. The calculated surface fields of the smooth and rough cavities are compared to determine the extent of the field enhancement, the area over which the enhancement is significant, and which surface features cause large field enhancement. We find that 1% of the surface analyzed has fields enhance by more than 45%. On average the Q-factor is increased by (3.8 ± 1.0) \%.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC027

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPLR047

Advanced Vertical Electro-Polishing studies at Cornell with Faraday

233

F. Furuta, M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, 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

Cornell's SRF group and Faraday Technology Inc. have started collaborations on two phase-II SBIR projects. Both projects are aiming for the development of advanced Vertical Electro-Polishing (VEP) for Nb SRF cavities, such as HF free or acid free VEP protocols. These could be eco-friendlier alternatives for the standard, HF-based EP electrolyte used, and could bring new breakthrough performance for Nb SRF cavities. Here we give a status update and report first results from these two projects.

Poster MOPLR047 [2.852 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR047

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUOP02

CBETA: The Cornell/BNL 4-Turn ERL with FFAG Return Arcs for eRHIC Prototyping

384

TUPLR002

use link to see paper's listing under its alternate paper code

G.H. Hoffstaetter, J. Barley, A.C. Bartnik, I.V. Bazarov, J. Dobbins, B.M. Dunham, R.G. Eichhorn, R.E. Gallagher, C.M. Gulliford, Y. Li, M. Liepe, W. Lou, C.E. Mayes, J.R. Patterson, D.M. Sabol, E.N. Smith, K.W. Smolenski
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I. Ben-Zvi, J.S. Berg, S.J. Brooks, G.J. Mahler, F. Méot, M.G. Minty, S. Peggs, V. Ptitsyn, T. Roser, D. Trbojevic, N. Tsoupas, J.E. Tuozzolo, H. Witte
BNL, Upton, Long Island, New York, USA
D. Douglas
JLab, Newport News, Virginia, USA

Cornell University has prototyped technology essential for any high brightness electron ERL. This includes a DC gun and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current CW cryomodule, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams, e.g. slid measurements for 6-D phase-space densities, a fast wire scanner for beam profiles, and beam loos diagnostics. All these are now available to equip a one-cryomodule ERL, and laboratory space has been cleared out and is radiation shielded to install this ERL at Cornell. BNL has designed a multi-turn ERL for eRHIC, where beam is transported more than 20 times around the RHIC tunnel. The number of transport lines is minimized by using two non-scaling (NS) FFAG arcs. A collaboration between BNL and Cornell has been formed to investigate the new NS-FFAG optics and the multi-turn eRHIC ERL design by building a 4-turn, one-cryomodule ERL at Cornell. It has a NS-FFAG return loop built with permanent magnets and is meant to accelerate 40mA beam to 200MeV.

Slides TUOP02 [7.848 MB]

Poster TUOP02 [13.981 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP02

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TUOP07

High Performance Next-Generation Nb3Sn Cavities for Future High Efficiency SRF Linacs

398

TUPRC031

use link to see paper's listing under its alternate paper code

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

Funding: DOE
A 1.3 GHz ILC-shape single-cell Nb3Sn cavity fabricated at Cornell has shown record performance, exceeding the cryogenic efficiency of niobium cavities at the gradients and quality factors demanded by some contemporary accelerator designs. An optimisation of the coating process has resulted in more cavities of the same design that achieve similar performance, proving the reproducibility of the method. In this paper, we discuss the current limitations on the peak accelerating gradients achieved by these cavities. In particular, high-pulsed-power RF testing, and thermometry mapping of the cavity during CW operation, are used to draw conclusions regarding the nature of the quench limitation. In light of these promising results, the feasibility and utility of applying the current state of the technology to a real-life application is discussed.

Slides TUOP07 [1.506 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP07

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPRC025

Low Temperature Nitrogen Baking of a Q0 SRF Cavities

472

P.N. Koufalis, F. Furuta, M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Nitrogen-doping has led to an unprecedented increase in the intrinsic quality factor of bulk-niobium superconducting RF cavities. So far, high temperature baking in a nitrogen atmosphere is used almost exclusively to dope cavities. Recently, we have set focus on low temperature baking to produce similar performance increases and we present those results here.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPRC025

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPLR010

Measurements and Analysis of Cavity Microphonics and Frequency Control in the Cornell ERL Main Linac Prototype Cryomodule

488

M. Ge, N. Banerjee, J. Dobbins, R.G. Eichhorn, F. Furuta, G.H. Hoffstaetter, M. Liepe, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The Cornell Main Linac cryomodule (MLC) is a key component in the CBETA project. The SRF cavities with high loaded-Q in the MLC are very sensitive to microphonics from mechanical vibrations. Poor frequency stability of the cavities would dramatically increase the input RF power required to maintain stable accelerating fields in the SRF cavities. In this paper, we present detailed results from microphonics measurement for the cavities in the MLC, discuss dominant vibration sources, and show vibration damping results. The current microphonics level meets the CBETA requirement of a 36MeV energy gain without applying fast tuner compensation.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR010

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPLR011

Performance of the Novel Cornell ERL Main Linac Prototype Cryomodule

492

F. Furuta, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, 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

The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based X-ray light source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Cavities have achieved the specification values of 16.2MV/m with high-Q of 2.0·10¹⁰ in 1.8K in continuous wave (CW) mode. During initial MLC cavity testing, we encountered some field emission, reducing Q and lowering quench field. To overcome field emission and find optimal cool-down parameters, RF processing and thermal cycles with different cool-down conditions has been done. Here we report on these studies and present final results from the MLC cavity performance.

Poster TUPLR011 [2.389 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR011

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPLR012

HOM Measurements for Cornell's ERL Main Linac Cryomodule

496

F. Furuta, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The main linac cryomodule (MLC) for a future energy-recovery linac (ERL) based X-ray source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. All HOMs in MLC have been scanned in 1.8K. The results show effective damping of HOMs, and also agree well with simulation results and the previous HOM scan results on one 7-cell cavity prototype test cryomodule. Here we present detailed results from these HOM studies.

Poster TUPLR012 [2.773 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR012

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPLR025

Optimal Nitrogen Doping Level to Reach High Q0

523

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

Funding: NSF and US DOE
New continuous wave (CW) accelerators such as LCLS-II at SLAC require many SRF cavities operating in the medium field region at unprecedented high Q. In order to achieve this demanding goal, nitrogen-doping of the SRF cavities will be used. Nitrogen-doping has been shown to affect the BCS resistance both by a lowering of Rbcs at low fields and by the introduction of an anti-Q slope which enables the Q to continue increasing as the RF field is increased. The exact strength of this anti-Q slope is heavily dependent on the doping recipe and specifically the mean free path of the RF penetration layer of the doped cavities. In addition to its effect on Rbcs, the mean free path affects the amount of residual resistance obtained due to trapped magnetic flux. We have analyzed nine cavities prepared with different levels of nitrogen-doping to understand how BCS and residual resistance are affected by changes in the mean free path. Here we present a model based on these experimental results to predict the optimal doping level to reach the maximum Q at 16 MV/m based on the ambient magnetic field conditions. We find that if the cavities can be cooled with small amounts of trapped flux, moderate nitrogen-doping is better, while if they will have large amounts of trapped flux, lighter dopings should be used.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR025

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRC015

Cool-Down Performance of the Cornell ERL Cryomodules

802

R.G. Eichhorn, F. Furuta, M. Ge, G.H. Hoffstaetter, M. Liepe, S.R. Markham, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich, D. Widger
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

In the framework of the ERL prototyping, Cornell University has built two cryomodules, one injector module and one prototype Main Linac Cryomodule (MLC). In 2015, the MLC was successfully cooled down for the first time. We will report details on the cool-down as well as cycle tests we did in order to achieve slow and fast cool-down of the cavities. We will also report on the improvement we made on the injector cryomodule which also included a modification of the heat exchanger can that allows now a more controlled cool-down, too.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPRC015

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)