SRF2015 - List of Authors (Crawford, A.C.)

Paper	Title	Page
MOPB028	Preservation of Very High Quality Factors of 1.3 GHz Nine Cell Cavities From Bare Vertical Test to Dressed Horizontal Test	149
	A. Grassellino, S. Aderhold, M. Checchin, A.C. Crawford, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, S. Posen, A.M. Rowe, D.A. Sergatskov, N. Solyak, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA D. Gonnella Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.M. Köszegi HZB, Berlin, Germany M. Liepe Cornell University, Ithaca, New York, USA
	In this contribution we will report quality factor evolution of several different nine cell N doped cavities with very high Q. The evolution of the quality factor will be reported from bare to dressed in vertical test to dressed in horizontal test with unity coupling to dressed in horizontal test and CM-like environment/configuration (with RF ancillaries). Cooling studies and optimal cooling regimes will be discussed for both vertical and horizontal tests and comparisons will be drawn also for different styles titanium vessels. Studies of sensitivities to magnetic field in final horizontal configuration have been performed by applying a field around the dressed cavity and varying the cooling; parameters required for a very good flux expulsion will be presented.
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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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MOPB087	Integrated High-Power Tests of Dressed N-doped 1.3 GHz SRF Cavities for LCLS-II	342
	N. Solyak, T.T. Arkan, B.E. Chase, A.C. Crawford, E. Cullerton, I.V. Gonin, A. Grassellino, C.J. Grimm, A. Hocker, J.P. Holzbauer, T.N. Khabiboulline, O.S. Melnychuk, J.P. Ozelis, T.J. Peterson, Y.M. Pischalnikov, K.S. Premo, A. Romanenko, A.M. Rowe, W. Schappert, D.A. Sergatskov, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA
	New auxiliary components have been designed and fabricated for the 1.3 GHz SRF cavities comprising the LCLS-II linac. In particular, the LCLS-II cavity’s helium vessel, high-power input coupler, higher-order mode (HOM) feedthroughs, magnetic shielding, and cavity tuning system were all designed to meet LCLS-II specifications. Integrated tests of the cavity and these components were done at Fermilab’s Horizontal Test Stand (HTS) using several kilowatts of continuous-wave (CW) RF power. The results of the tests are summarized here.
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MOPB104	Flux Expulsion Variation in SRF Cavities	404
	S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	Treating a cavity with nitrogen doping significantly increases Q₀ at medium fields, reducing cryogenic costs for high duty factor linear accelerators such as LCLS II. N-doping also makes cavities more sensitive to increased residual resistance due to trapped magnetic flux, making it critical to either have extremely effective magnetic shielding, or to prevent flux from being trapped in the cavity during cooldown. In this paper, we report on results of a study of flux expulsion. We discuss possible ways in which flux can be pinned in the inner surface, outer surface, or bulk of a cavity, and we present experimental results studying these mechanisms. We show that grain structure appears to play a key role and that a cavity that expelled flux poorly changed to expelling flux well after a high temperature furnace treatment. We further show that after furnace treatment, this cavity exhibited a significant improvement in quality factor when cooled in an external magnetic field. We conclude with implications for SRF accelerators with high Q₀ requirements.
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MOPB111	Furnace N2 Doping Treatments at Fermilab	423
	M. Merio, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, A.M. Rowe, M. Wong Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. The Fermilab SRF group regularly performs Nitrogen (N2) doping heat treatments on superconducting cavities in order to improve their Radio Frequency (RF) performances. This paper describes the set up and operations of the Fermilab vacuum furnaces, with a major focus on the implementation and execution of the N2 doping recipe. The cavity preparation will be presented, N2 doping recipes will be analyzed and heat treatment data will be reported in the form of plot showing temperature, total pressure and partial pressures over time. Finally possible upgrades and improvements of the furnace and the N2 doping process are discussed.
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TUPB099	Magnetic Foils for SRF Cryomodule	844
	G. Wu, S. Aderhold, S.K. Chandrasekaran, A.C. Crawford, A. Grassellino, C.J. Grimm, J.P. Ozelis, D.A. Sergatskov, A. Vostrikov Fermilab, Batavia, Illinois, USA
	Funding: Work supported by FRA under DOE contract DE-AC02-07CH11359 High quality factor niobium cavities require minimal residual magnetic field around the high magnetic field region. A typical global magnetic shield takes more material and provides less effective magnetic screening. On the other hand, local magnetic shield has to introduce complex geometries to cover access ports and instrumentation and thermal straps. Local magnetic source and thermal current will increase residual field seen by SRF cavities regardless the complexity of local magnetic shield. Magnetic foils that is cryogenic compatible provides a great benefit to reduce residual magnetic field. This paper will describe the evaluation of such magnetic foils in both vertical and horizontal test.
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Paper

Title

Page

Preservation of Very High Quality Factors of 1.3 GHz Nine Cell Cavities From Bare Vertical Test to Dressed Horizontal Test

149

A. Grassellino, S. Aderhold, M. Checchin, A.C. Crawford, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, S. Posen, A.M. Rowe, D.A. Sergatskov, N. Solyak, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA
D. Gonnella
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.M. Köszegi
HZB, Berlin, Germany
M. Liepe
Cornell University, Ithaca, New York, USA

In this contribution we will report quality factor evolution of several different nine cell N doped cavities with very high Q. The evolution of the quality factor will be reported from bare to dressed in vertical test to dressed in horizontal test with unity coupling to dressed in horizontal test and CM-like environment/configuration (with RF ancillaries). Cooling studies and optimal cooling regimes will be discussed for both vertical and horizontal tests and comparisons will be drawn also for different styles titanium vessels. Studies of sensitivities to magnetic field in final horizontal configuration have been performed by applying a field around the dressed cavity and varying the cooling; parameters required for a very good flux expulsion will be presented.

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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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MOPB087

Integrated High-Power Tests of Dressed N-doped 1.3 GHz SRF Cavities for LCLS-II

342

N. Solyak, T.T. Arkan, B.E. Chase, A.C. Crawford, E. Cullerton, I.V. Gonin, A. Grassellino, C.J. Grimm, A. Hocker, J.P. Holzbauer, T.N. Khabiboulline, O.S. Melnychuk, J.P. Ozelis, T.J. Peterson, Y.M. Pischalnikov, K.S. Premo, A. Romanenko, A.M. Rowe, W. Schappert, D.A. Sergatskov, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA

New auxiliary components have been designed and fabricated for the 1.3 GHz SRF cavities comprising the LCLS-II linac. In particular, the LCLS-II cavity’s helium vessel, high-power input coupler, higher-order mode (HOM) feedthroughs, magnetic shielding, and cavity tuning system were all designed to meet LCLS-II specifications. Integrated tests of the cavity and these components were done at Fermilab’s Horizontal Test Stand (HTS) using several kilowatts of continuous-wave (CW) RF power. The results of the tests are summarized here.

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MOPB104

Flux Expulsion Variation in SRF Cavities

404

S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

Treating a cavity with nitrogen doping significantly increases Q₀ at medium fields, reducing cryogenic costs for high duty factor linear accelerators such as LCLS II. N-doping also makes cavities more sensitive to increased residual resistance due to trapped magnetic flux, making it critical to either have extremely effective magnetic shielding, or to prevent flux from being trapped in the cavity during cooldown. In this paper, we report on results of a study of flux expulsion. We discuss possible ways in which flux can be pinned in the inner surface, outer surface, or bulk of a cavity, and we present experimental results studying these mechanisms. We show that grain structure appears to play a key role and that a cavity that expelled flux poorly changed to expelling flux well after a high temperature furnace treatment. We further show that after furnace treatment, this cavity exhibited a significant improvement in quality factor when cooled in an external magnetic field. We conclude with implications for SRF accelerators with high Q₀ requirements.

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MOPB111

Furnace N2 Doping Treatments at Fermilab

423

M. Merio, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, A.M. Rowe, M. Wong
Fermilab, Batavia, Illinois, USA
M. Checchin, M. Martinello
Illinois Institute of Technology, Chicago, Illlinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
The Fermilab SRF group regularly performs Nitrogen (N2) doping heat treatments on superconducting cavities in order to improve their Radio Frequency (RF) performances. This paper describes the set up and operations of the Fermilab vacuum furnaces, with a major focus on the implementation and execution of the N2 doping recipe. The cavity preparation will be presented, N2 doping recipes will be analyzed and heat treatment data will be reported in the form of plot showing temperature, total pressure and partial pressures over time. Finally possible upgrades and improvements of the furnace and the N2 doping process are discussed.

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TUPB099

Magnetic Foils for SRF Cryomodule

844

G. Wu, S. Aderhold, S.K. Chandrasekaran, A.C. Crawford, A. Grassellino, C.J. Grimm, J.P. Ozelis, D.A. Sergatskov, A. Vostrikov
Fermilab, Batavia, Illinois, USA

Funding: Work supported by FRA under DOE contract DE-AC02-07CH11359
High quality factor niobium cavities require minimal residual magnetic field around the high magnetic field region. A typical global magnetic shield takes more material and provides less effective magnetic screening. On the other hand, local magnetic shield has to introduce complex geometries to cover access ports and instrumentation and thermal straps. Local magnetic source and thermal current will increase residual field seen by SRF cavities regardless the complexity of local magnetic shield. Magnetic foils that is cryogenic compatible provides a great benefit to reduce residual magnetic field. This paper will describe the evaluation of such magnetic foils in both vertical and horizontal test.

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