IPAC2017 - List of Authors (Hall, D.L.)

Paper	Title	Page
MOOCA2	First Results From New Single-Cell Nb3Sn Cavities Coated at Cornell University	40
	D.L. Hall, J.J. Kaufman, M. Liepe, R.D. Porter, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cavities coated with Nb3Sn at Cornell University demonstrate quality factors of >10¹⁰ at 4.2 K, outperforming equivalent niobium cavities by a factor of >30 at these bath temperatures. These quality factors have been maintained up to fields of 17-18 MV/m without significant Q-slope. Recently, new single-cell cavities have been added to the Cornell Nb3Sn programme in an effort to improve statistics and allow further exploration of the available parameter space. In this paper we report on the first results of these new cavities, as well as the latest performance from other cavities already in use on the programme. Furthermore, continuing work to optimise the coating procedure is reported on, and the latest understanding of the ideal coating profile is discussed.
	Slides MOOCA2 [10.366 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOOCA2
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MOPVA115	Status and Challenges of Vertical Electro-Polishing R&D at Cornell	1115
	F. Furuta, M. Ge, T. Gruber, D.L. Hall, J.J. Kaufman, M. Liepe, R.D. Porter, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan T.D. Hall, M.E. Inman, R. Radhakrishnan, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA H. Hayano, S. Kato, T. Saeki KEK, Ibaraki, Japan
	Advanced Vertical Electro-Polishing (VEP) R&D for SRF Niobium cavities continues at Cornell's SRF group. One focus of this work is new EP cathode development in collaboration with KEK and Marui Galvanizing Co. Ltd (Marui) in Japan, and another focus is on HF free or acid free VEP protocols in collaboration with Faraday Technology Inc. The outcomes of these activities could be a significant cost reduction and an environmentally-friendlier VEP, which would be a breakthrough for future large scale EP applications on SRF cavities. Here we give a status update and report latest results from these R&D activities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA115
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MOPVA116	Quench Studies in Single-Cell Nb3Sn Cavities Coated Using Vapour Diffusion	1119
	D.L. Hall, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA P. Cueva, D. Liarte, D.A. Muller, J.P. Sethna Cornell University, Ithaca, New York, USA
	The superconductor Nb3Sn is known to have a superheating field, Hsh, of approximately 400 mT. This critical field represents the ultimate achievable gradient in a superconducting cavity, and is equivalent to an accelerating gradient of 90 MV/m in an ILC single-cell cavity for this value of Hsh. However, the currently best performing Nb3Sn single-cell cavities remain limited to accelerating gradients of 17-18 MV/m, translating to a peak surface magnetic field of approx. 70 mT. In this paper, we consider theoretical models of candidate quench mechanisms, and compare them to experimental data from surface analysis and cavity tests.
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MOPVA117	Performance of a SRF Half-Wave-Resonator Tested at Cornell for the RAON Project	1123
	M. Ge, F. Furuta, T. Gruber, D.L. Hall, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	A prototype half-wave-resonator (HWR) with frequency 162.5MHz and geometrical \beta=0.12 for the RAON project is currently undergoing testing at Cornell University. Detailed vertical performance testing includes (1) test of the bare cavity without the helium tank; (2) test of the dressed cavity with helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis.
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MOPVA118	Impact of Trapped Magnetic Flux and Thermal Gradients on the Performance of Nb3Sn Cavities	1127
SUSPSIK103	use link to see paper's listing under its alternate paper code
	D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA D. Liarte, J.P. Sethna Cornell University, Ithaca, New York, USA
	Trapped magnetic flux is known to degrade the quality factor of superconducting cavities by increasing the surface losses ascribed to the residual resistance. In Nb3Sn cavities, which consist of a thin layer of Nb3Sn coated on a bulk niobium substrate, the bimetallic interface results in a thermal current being generated in the presence of a thermal gradient, which will in turn generate flux that can be trapped. In this paper we quantify the impact of trapped flux, from either ambient fields or thermal gradients, on the performance of the cavity. We discover that the sensitivity to trapped flux, a measure of the increase in residual resistance as a function of the amount of flux trapped, is a function of the accelerating gradient. A theoretical framework to explain this phenomenon is proposed, and the impact on the requirements for operating a Nb3Sn cavity in a cryomodule are considered.
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MOPVA119	Surface Analysis of Features Seen on Nb3Sn Sample Coupons Grown by Vapour Diffusion	1130
	D.L. Hall, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Arias, P. Cueva, D.A. Muller, N. Sitaraman Cornell University, Ithaca, New York, USA
	As a high-kappa superconductor with a coherence length of 7 nm, the superconductor Nb3Sn is highly susceptible to material features at the sub-micron scale. For niobium surfaces coated with a thin layer of Nb3Sn using the vapour diffusion method, the polycrystalline nature of the film grown lends to the possibility that performance-degrading non-uniformities may develop. In particular, regions of insufficiently thick coating and tin-depletion have been seen to occur in sample coupons. In the interests of understanding how to control the presence and nature of such features, it is necessary to know how they form. In this paper we stop the coating at defined instances to gain a stop-motion image of the growth of the layer, and use SEM and TEM techniques to image the development of the features seen in previously coated samples. We demonstrate that surface pre-anodisation can suppress the formation of thin film regions, and apply this technique to a single-cell cavity. Contemporarily, we use TEM with EDS mapping to monitor grain boundaries and tin-depleted regions within the layer.
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MOPVA121	Frequency Tuner Development at Cornell for the RAON Half-Wave-Resonator	1134
	M. Ge, F. Furuta, T. Gruber, D.L. Hall, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	The half-wave-resonators (HWR) for the RAON pro-ject require a slow frequency tuner that can provide at least 80 kHz tuning range. Cornell University is currently in the process of designing, prototyping, and testing this HWR tuner. In this paper, we present the tuner design, prototype fabrication, and first test results.
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MOPVA122	Microphonics Studies of the CBETA Linac Cryomodules	1138
	N. Banerjee, J. Dobbins, F. Furuta, D.L. Hall, G.H. Hoffstaetter, M. Liepe, P. Quigley, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was performed through the support of NYSERDA (New York State Energy Research and Development Agency). The Cornell BNL ERL Test Accelerator (CBETA) incorporates two SRF linacs; one for its injector and another for the energy recovery loop. Microphonics in both the cryomodules play a crucial role in determining the energy stability of the electron beam in high current operation. We have measured vibrations and frequency detuning of the SRF cavities and determined that the cryogenic system is the major source of microphonics in both cryomodules. In this paper we discuss these measurements and demonstrate an Active Microphonics Compensation system implemented using fast piezo-electric tuners which we incorporated in our Low Level RF control system to be used in routine operation.
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MOPVA123	Cornell Sample Host Cavity: Recent Results	1142
	J.T. Maniscalco, D.L. Hall, M. Liepe, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V.M. Arrieta, S.R. McNeal, W.E. Williams Ultramet, Pacoima, California, USA
	Funding: NSF-PHY 1416318 NSF-PHY 1549132 The Cornell sample host cavity is a 3.9~GHz testing system for RF analysis of novel superconducting surfaces. The cavity applies fields up to 100~mT on a removable and replaceable 5-inch sample plate in order to measure the surface resistance of the material under investigation. The cavity also includes a temperature-mapping system for localization of quench events and surface defects. In this paper, we present recent experimental results from the host cavity of niobium deposited onto molybdenum and copper substrates using chemical vapor deposition, in collaboration with industry partner Ultramet. The results indicate low BCS resistance and good adhesion but also areas of high residual resistance due to chemical and morphological defects.
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MOPVA124	Effectiveness of Chemical Treatments for Reducing the Surface Roughness of Nb3Sn	1145
SUSPSIK104	use link to see paper's listing under its alternate paper code
	R.D. Porter, F. Furuta, 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 DE-SC008431, NSF-PHY 1549132, NSF DMR-1120296 Current Niobium-3 Tin (Nb3Sn) superconducting radio-frequency (SRF) accelerator cavities have rougher surfaces than conventional electropolished Niobium accelerator cavities. The surface roughness can cause enhancement of the surface magnetic field, pushing it beyond the critical field. If this occurs over a large enough area it can cause the cavity to quench. The surface roughness may cause other effects that negatively impact cavity quality factor (Q) performance. Reducing surface roughness of Nb3Sn cavities may be necessary to achieve higher gradient with high Q. Current chemical treatments for reducing the surface roughness of Niobium are challenging for Nb3Sn: the Nb3Sn layer is only ~2 um thick while it is difficult to remove less than 1 mu uniformly with most chemical treatments. This paper presents measurements of the surface roughness before and after Buffered Chemical Polish, Electropolishing and oxipolishing.
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WEPIK036	ERL Cryomodule Testing and Beam Capabilities	3010
	F. Furuta, N. Banerjee, J. Dobbins, R.G. Eichhorn, M. Ge, D.L. Hall, G.H. Hoffstaetter, M. Liepe, R.D. Porter, 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) prototype is a key component for the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simul-taneously for high efficient SRF cavity operation and for supporting very high CW beam currents. Initial MLC testing has demonstrated that cavity performance and HOMs damping meet specification values. Recent, addi-tional tests have focused on RF field stability, and cavity microphonics. In this paper, we summarize the perfor-mance of this novel ERL cryomodule and evaluate its beam capabilities based on the measured performance.
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WEPVA145	Analysis of Mean Free Path and Field Dependent Surface Resistance	3609
	J.T. Maniscalco, F. Furuta, D.L. Hall, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF-PHY 1416318 Work from Cornell in 2016 built on recent theoretical research in the field of SRF to link the electron mean free path to the field-dependent BCS surface resistance. This research relates the magnitude of the ‘‘anti-Q-slope'', the puzzling reduction of surface resistance with increasing RF field intensity observed in certain cavities, to the doping level of nitrogen-doped niobium, quantified by the mean free path: shorter mean free paths correspond directly with stronger anti-Q-slopes. The theoretical connection comes through the overheating of the quasiparticles, which more effectively transfer their energy to the lattice at short mean free paths. In this report, we present an update of this analysis, investigating recent test results of low-temperature-doped single-cell and nine-cell cavities. We also study the theoretical implications for cavities at frequencies higher and lower than the often-studied 1.3~GHz.
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Paper

Title

Page

First Results From New Single-Cell Nb3Sn Cavities Coated at Cornell University

40

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

Cavities coated with Nb3Sn at Cornell University demonstrate quality factors of >10¹⁰ at 4.2 K, outperforming equivalent niobium cavities by a factor of >30 at these bath temperatures. These quality factors have been maintained up to fields of 17-18 MV/m without significant Q-slope. Recently, new single-cell cavities have been added to the Cornell Nb3Sn programme in an effort to improve statistics and allow further exploration of the available parameter space. In this paper we report on the first results of these new cavities, as well as the latest performance from other cavities already in use on the programme. Furthermore, continuing work to optimise the coating procedure is reported on, and the latest understanding of the ideal coating profile is discussed.

Slides MOOCA2 [10.366 MB]

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MOPVA115

Status and Challenges of Vertical Electro-Polishing R&D at Cornell

1115

F. Furuta, M. Ge, T. Gruber, D.L. Hall, J.J. Kaufman, M. Liepe, R.D. Porter, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
T.D. Hall, M.E. Inman, R. Radhakrishnan, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
H. Hayano, S. Kato, T. Saeki
KEK, Ibaraki, Japan

Advanced Vertical Electro-Polishing (VEP) R&D for SRF Niobium cavities continues at Cornell's SRF group. One focus of this work is new EP cathode development in collaboration with KEK and Marui Galvanizing Co. Ltd (Marui) in Japan, and another focus is on HF free or acid free VEP protocols in collaboration with Faraday Technology Inc. The outcomes of these activities could be a significant cost reduction and an environmentally-friendlier VEP, which would be a breakthrough for future large scale EP applications on SRF cavities. Here we give a status update and report latest results from these R&D activities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA115

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MOPVA116

Quench Studies in Single-Cell Nb3Sn Cavities Coated Using Vapour Diffusion

1119

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

The superconductor Nb3Sn is known to have a superheating field, Hsh, of approximately 400 mT. This critical field represents the ultimate achievable gradient in a superconducting cavity, and is equivalent to an accelerating gradient of 90 MV/m in an ILC single-cell cavity for this value of Hsh. However, the currently best performing Nb3Sn single-cell cavities remain limited to accelerating gradients of 17-18 MV/m, translating to a peak surface magnetic field of approx. 70 mT. In this paper, we consider theoretical models of candidate quench mechanisms, and compare them to experimental data from surface analysis and cavity tests.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA116

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MOPVA117

Performance of a SRF Half-Wave-Resonator Tested at Cornell for the RAON Project

1123

M. Ge, F. Furuta, T. Gruber, D.L. Hall, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

A prototype half-wave-resonator (HWR) with frequency 162.5MHz and geometrical \beta=0.12 for the RAON project is currently undergoing testing at Cornell University. Detailed vertical performance testing includes (1) test of the bare cavity without the helium tank; (2) test of the dressed cavity with helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA117

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MOPVA118

Impact of Trapped Magnetic Flux and Thermal Gradients on the Performance of Nb3Sn Cavities

1127

SUSPSIK103

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

D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
D. Liarte, J.P. Sethna
Cornell University, Ithaca, New York, USA

Trapped magnetic flux is known to degrade the quality factor of superconducting cavities by increasing the surface losses ascribed to the residual resistance. In Nb3Sn cavities, which consist of a thin layer of Nb3Sn coated on a bulk niobium substrate, the bimetallic interface results in a thermal current being generated in the presence of a thermal gradient, which will in turn generate flux that can be trapped. In this paper we quantify the impact of trapped flux, from either ambient fields or thermal gradients, on the performance of the cavity. We discover that the sensitivity to trapped flux, a measure of the increase in residual resistance as a function of the amount of flux trapped, is a function of the accelerating gradient. A theoretical framework to explain this phenomenon is proposed, and the impact on the requirements for operating a Nb3Sn cavity in a cryomodule are considered.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA118

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MOPVA119

Surface Analysis of Features Seen on Nb3Sn Sample Coupons Grown by Vapour Diffusion

1130

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

As a high-kappa superconductor with a coherence length of 7 nm, the superconductor Nb3Sn is highly susceptible to material features at the sub-micron scale. For niobium surfaces coated with a thin layer of Nb3Sn using the vapour diffusion method, the polycrystalline nature of the film grown lends to the possibility that performance-degrading non-uniformities may develop. In particular, regions of insufficiently thick coating and tin-depletion have been seen to occur in sample coupons. In the interests of understanding how to control the presence and nature of such features, it is necessary to know how they form. In this paper we stop the coating at defined instances to gain a stop-motion image of the growth of the layer, and use SEM and TEM techniques to image the development of the features seen in previously coated samples. We demonstrate that surface pre-anodisation can suppress the formation of thin film regions, and apply this technique to a single-cell cavity. Contemporarily, we use TEM with EDS mapping to monitor grain boundaries and tin-depleted regions within the layer.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA119

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MOPVA121

Frequency Tuner Development at Cornell for the RAON Half-Wave-Resonator

1134

M. Ge, F. Furuta, T. Gruber, D.L. Hall, S.W. Hartman, C. Henderson, M. Liepe, S. Lok, T.I. O'Connell, P.J. Pamel, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

The half-wave-resonators (HWR) for the RAON pro-ject require a slow frequency tuner that can provide at least 80 kHz tuning range. Cornell University is currently in the process of designing, prototyping, and testing this HWR tuner. In this paper, we present the tuner design, prototype fabrication, and first test results.

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MOPVA122

Microphonics Studies of the CBETA Linac Cryomodules

1138

N. Banerjee, J. Dobbins, F. Furuta, D.L. Hall, G.H. Hoffstaetter, M. Liepe, P. Quigley, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was performed through the support of NYSERDA (New York State Energy Research and Development Agency).
The Cornell BNL ERL Test Accelerator (CBETA) incorporates two SRF linacs; one for its injector and another for the energy recovery loop. Microphonics in both the cryomodules play a crucial role in determining the energy stability of the electron beam in high current operation. We have measured vibrations and frequency detuning of the SRF cavities and determined that the cryogenic system is the major source of microphonics in both cryomodules. In this paper we discuss these measurements and demonstrate an Active Microphonics Compensation system implemented using fast piezo-electric tuners which we incorporated in our Low Level RF control system to be used in routine operation.

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MOPVA123

Cornell Sample Host Cavity: Recent Results

1142

J.T. Maniscalco, D.L. Hall, M. Liepe, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V.M. Arrieta, S.R. McNeal, W.E. Williams
Ultramet, Pacoima, California, USA

Funding: NSF-PHY 1416318 NSF-PHY 1549132
The Cornell sample host cavity is a 3.9~GHz testing system for RF analysis of novel superconducting surfaces. The cavity applies fields up to 100~mT on a removable and replaceable 5-inch sample plate in order to measure the surface resistance of the material under investigation. The cavity also includes a temperature-mapping system for localization of quench events and surface defects. In this paper, we present recent experimental results from the host cavity of niobium deposited onto molybdenum and copper substrates using chemical vapor deposition, in collaboration with industry partner Ultramet. The results indicate low BCS resistance and good adhesion but also areas of high residual resistance due to chemical and morphological defects.

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MOPVA124

Effectiveness of Chemical Treatments for Reducing the Surface Roughness of Nb3Sn

1145

SUSPSIK104

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

R.D. Porter, F. Furuta, 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 DE-SC008431, NSF-PHY 1549132, NSF DMR-1120296
Current Niobium-3 Tin (Nb3Sn) superconducting radio-frequency (SRF) accelerator cavities have rougher surfaces than conventional electropolished Niobium accelerator cavities. The surface roughness can cause enhancement of the surface magnetic field, pushing it beyond the critical field. If this occurs over a large enough area it can cause the cavity to quench. The surface roughness may cause other effects that negatively impact cavity quality factor (Q) performance. Reducing surface roughness of Nb3Sn cavities may be necessary to achieve higher gradient with high Q. Current chemical treatments for reducing the surface roughness of Niobium are challenging for Nb3Sn: the Nb3Sn layer is only ~2 um thick while it is difficult to remove less than 1 mu uniformly with most chemical treatments. This paper presents measurements of the surface roughness before and after Buffered Chemical Polish, Electropolishing and oxipolishing.

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WEPIK036

ERL Cryomodule Testing and Beam Capabilities

3010

F. Furuta, N. Banerjee, J. Dobbins, R.G. Eichhorn, M. Ge, D.L. Hall, G.H. Hoffstaetter, M. Liepe, R.D. Porter, 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) prototype is a key component for the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simul-taneously for high efficient SRF cavity operation and for supporting very high CW beam currents. Initial MLC testing has demonstrated that cavity performance and HOMs damping meet specification values. Recent, addi-tional tests have focused on RF field stability, and cavity microphonics. In this paper, we summarize the perfor-mance of this novel ERL cryomodule and evaluate its beam capabilities based on the measured performance.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK036

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WEPVA145

Analysis of Mean Free Path and Field Dependent Surface Resistance

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

Funding: NSF-PHY 1416318
Work from Cornell in 2016 built on recent theoretical research in the field of SRF to link the electron mean free path to the field-dependent BCS surface resistance. This research relates the magnitude of the ‘‘anti-Q-slope'', the puzzling reduction of surface resistance with increasing RF field intensity observed in certain cavities, to the doping level of nitrogen-doped niobium, quantified by the mean free path: shorter mean free paths correspond directly with stronger anti-Q-slopes. The theoretical connection comes through the overheating of the quasiparticles, which more effectively transfer their energy to the lattice at short mean free paths. In this report, we present an update of this analysis, investigating recent test results of low-temperature-doped single-cell and nine-cell cavities. We also study the theoretical implications for cavities at frequencies higher and lower than the often-studied 1.3~GHz.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA145

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