IPAC2018 - List of Authors (Liepe, M.)

Paper	Title	Page
TUYGBE2	CBETA, the 4-Turn ERL with SRF and Single Return Loop	635
	G.H. Hoffstaetter, N. Banerjee, J. Barley, A.C. Bartnik, I.V. Bazarov, D.C. Burke, J.A. Crittenden, L. Cultrera, J. Dobbins, S.J. Full, F. Furuta, R.E. Gallagher, M. Ge, C.M. Gulliford, B.K. Heltsley, R.P.K. Kaplan, V.O. Kostroun, Y. Li, M. Liepe, W. Lou, C.E. Mayes, J.R. Patterson, P. Quigley, D.M. Sabol, D. Sagan, J. Sears, C.H. Shore, E.N. Smith, K.W. Smolenski, V. Veshcherevich, D. Widger Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.S. Berg, S.J. Brooks, C. Liu, G.J. Mahler, F. Méot, R.J. Michnoff, M.G. Minty, S. Peggs, V. Ptitsyn, T. Roser, P. Thieberger, D. Trbojevic, N. Tsoupas, J.E. Tuozzolo, F.J. Willeke, H. Witte BNL, Upton, Long Island, New York, USA D. Douglas JLab, Newport News, Virginia, USA J.K. Jones Cockcroft Institute, Warrington, Cheshire, United Kingdom D. Jusic Cornell University, Ithaca, New York, USA D.J. Kelliher STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom B.C. Kuske, M. McAteer, J. Völker HZB, Berlin, Germany
	Funding: Supported by NSF award DMR-0807731, DOE grant DE-AC02-76SF00515, and NYSERDA. A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. This technique will be tested in CBETA, which has a single return for the 4-beam energies with strongly-focusing permanent magnets of Halbach type. The high-brightness beam with 150~MeV and up to 40~mA will have applications beyond accelerator research, in industry, in nuclear physics, and in X-ray science. Low current electron beam has already been sent through the most relevant parts of CBETA, from the DC gun through both cryomodules, through one of the 8 similar separator lines, and through one of the 27 similar FFA structures. Further construction is envisioned to lead to a commissioning start for the full system early in 2019.
	Slides TUYGBE2 [17.343 MB]
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WEPMF036	RF Test Result of a BNL N-Doped 500 MHz B-Cell Cavity at Cornell	2440
	F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA F. Gao, J. Rose BNL, Upton, Long Island, New York, USA
	Cornell's SRF group has collaborated with Brookhaven National Laboratory (BNL) on one 500 MHz CESR type SRF "B-cell" cavity (BNL B-cell) for the National Synchrotron Light Source II. Cornell has been responsible for RF surface preparation, vertical testing, and short cavity string assembly. As a state-of-the-art surface preparation protocol, Cornell selected Nitrogen doping for the BNL B-cell. N-doping has been well demonstrated and established to push the cavity quality factor (Q0) higher in 1.3GHz SRF cavities at many laboratories. Cornell calculated that N-doping could also be beneficial on a 500MHz SRF cavity, with a potential to increase its Q0 by a factor of two compared with the traditional chemical polishing based surface preparation protocol. Here we report on the detailed surface preparation and vertical test result of the BNL B-cell.
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WEPMF037	HF Free Bipolar Electro-Polishing Studies on Niobium SRF Cavities at Cornell With Faraday Technology	2443
	F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, P.N. Koufalis, 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, R. Radhakrishnan, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA
	Cornell's SRF group and Faraday Technology have been collaborating on two phase-II SBIR projects. One of them is the development and commissioning of a 9-cell scale HF free Bipolar Electro-Polishing (BEP) system. Faraday Technology has upgraded their 1.3 GHz single-cell BEP system for hosting 9-cell cavities. Initial commissioning of the new system was done with a three single-cell cavity string, and high a gradient of 40MV/m was demonstrated during the RF tests at Cornell. After this success with the test string, the 9-cell cavity was processed with the new system at Faraday and RF test was performed at Cornell. Here we report detailed results from these 9-cell scale HF free BEP studies.
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WEPMF038	Microphonics Suppression in the CBETA Linac Cryomodules	2447
SUSPL068	use link to see paper's listing under its alternate paper code
	N. Banerjee, J. Dobbins, F. Furuta, G.H. Hoffstaetter, R.P.K. Kaplan, 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 New York State Energy Research and Development Agency. The linac cryomodules were constructed with funding from the National Science Foundation. The Cornell-BNL ERL Test Accelerator (CBETA) is a new multi-turn energy recovery linac currently under construction at Cornell University. It uses two superconducting linacs, both of which are susceptible to microphonics detuning. The high-current injector accelerates electrons to 6 MeV and the main linac accelerates and decelerates electrons by 36 MeV. In this paper, we discuss various measures taken to reduce vibrations caused by instabilities and flow transients in the cryogenic system of the main linac cryomodule. We further describe the use of a Least Mean Square algorithm in establishing a stable Active Microphonics Compensation system for operation of the main linac cavities.
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WEPMF039	Experimental Results on the Field and Frequency Dependence of the Surface Resistance of Niobium Cavities	2451
	P.N. Koufalis, M. Liepe, J.T. Maniscalco, T.E. Oseroff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We investigate the field and frequency dependence of the surface resistance of single-cell niobium cavities as a function of surface treatment at 1.3, 2.6, and 3.9 GHz. The surface resistance is broken down into two parts: the temperature-independent residual resistance and the temperature-dependent BCS resistance. While the low-field BCS resistance is known to vary quadratically with frequency, the exact dependence of the BCS and residual resistances on field at higher frequencies are important topics for further investigation. We offer results on a systematic experimental study of the residual and BCS resistance as a function of frequency and field for clean niobium and high-temperature nitrogen-doped niobium.
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WEPMF041	Insights into the Role of C, N, and O Introduced by Low Temperature Baking on Niobium Cavity Performance	2455
SUSPL072	use link to see paper's listing under its alternate paper code
	P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Previous experiments have shown that introducing nitrogen gas during low temperature bakes (120-160 C) of niobium cavities introduces C, N, and O impurities to the first 10-100 nm of the surface. This new treatment results in higher quality factors and even 'anti-Q-slope' in some cases. However, it is not entirely clear the role that each of these impurities plays in the performance enhancement of the cavities. It has been suggested that interstitial N within the first few nm of the surface is solely responsible for the observed enhancement, but little work has been done on the role of C and O. Because both C and O are abundant in much higher quantities than N near the surface, it is important to understand whether they are beneficial or detrimental to cavity performance. We provide further insight into the effects of C and O on cavity performance by baking in an ambient atmosphere rich in CO2 as opposed to N2.
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WEPMF042	A Computational Method for More Accurate Measurements of the Surface Resistance in SRF Cavities	2458
	J.T. Maniscalco, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The principal loss mechanism for superconducting RF cavities in normal operation is Ohmic heating due to the microwave surface resistance in the superconducting surface. The typical method for calculating this field-dependent surface resistance R_s(H) from RF measurements of quality factor Q₀ implicitly returns a weighted average of R_s over the surface as a function of peak surface magnetic field H, not the true value of R_s as a function of the local magnitude of H. In this work we present a computational method to convert a measured Q₀ vs. H_peak to a more accurate R_s vs. H_local, given knowledge about cavity geometry and field distribution.
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WEPMF043	Frequency Tuner Development at Cornell for the RAON Half Wave Resonators	2461
	M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, 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
	The superconducting half-wave-resonators for the RAON project require a slow frequency tuner that can provide at least 80 kHz tuning range. Cornell University has designed, prototyped, and tested a tuner for these half-wave-resonators. In this paper, we present the tuner design, prototype fabrication, test insert preparation, long-term testing and tuner performance test results at cryogenic temperature. The performance of the tuner is analyzed in detail.
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WEPMF044	Updates on the DC Field Dependence Cavity	2465
	J.T. Maniscalco, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Work at Cornell has demonstrated good agreement between a theoretical model by A. Gurevich of the anti-Q-slope (a field-dependent decrease of the microwave surface resistance) and experimental results from impurity-doped niobium. As a corollary, the model predicts that a strong DC magnetic field applied parallel to the RF surface will produce a similar decrease in surface resistance. In order to explore this prediction for many materials, we have designed a new coaxial cavity with a strong, uniform DC field superimposed over a weak RF field on a removable and replaceable niobium sample. Here we present updates on the progress of this new cavity.
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WEPMF045	Performance of the Prototype SRF Half-Wave-Resonators Tested at Cornell for the RAON Project	2468
	M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, 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
	Two prototype superconducting half-wave-resonator (162.5 MHz and β=0.12) for the RAON project have been successfully tested at Cornell University. Detailed vertical performance testing included (1) test of the bare cavity without the helium tank, and (2) test of the dressed cavity with a helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis, showing that the specifications for RAON were met.
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WEPMF046	Modeling of the Frequency and Field Dependence of the Surface Resistance of Impurity-Doped Niobium	2471
SUSPL073	use link to see paper's listing under its alternate paper code
	J.T. Maniscalco, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The anti-Q-slope, a field-dependent decrease in surface resistance observed in impurity-doped niobium, has been investigated extensively in 1.3 GHz cavities. New early research into this effect has recently been performed at higher and lower frequencies, revealing an additional dependence on frequency: the anti-Q-slope is stronger at higher frequencies and weaker at lower frequencies. Several models have been proposed to explain the anti-Q-slope, with varying success in this new frequency-dependent regime. In this work, we analyze recent experimental data from a low-temperature-doped 1.3 GHz cavity and a high-temperature nitrogen-doped 2.6 GHz cavity and discuss the implications of these results on the proposed models.
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WEPMF047	Performance of Samples With Novel SRF Materials and Growth Techniques	2475
SUSPL074	use link to see paper's listing under its alternate paper code
	T.E. Oseroff, M. Ge, M. Liepe, J.T. Maniscalco, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA S.R. McNeal Ultramet, Pacoima, California, USA M.J. Sowa Veeco-CNT, Medford, USA
	Novel materials are currently being studied in an attempt to push accelerating superconducting RF cavities to support higher accelerating fields and to operate with lower power loss. Growing layers of these materials of the quality necessary has proven to be difficult. In this work, we present the SRF performance of planar samples of the promising materials, NbN and Nb¬3Sn, grown using atomic layer deposition (ALD) and chemical vapor deposition (CVD) respectively. Results are promising.
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WEPMF050	Update on Nb3Sn Progress at Cornell University	2479
	R.D. Porter, J. Ding, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.A. Arias, P. Cueva, D.A. Muller, N. Sitaraman Cornell University, Ithaca, New York, USA
	Niobium-3 Tin (Nb3Sn) is the most promising alternative material for SRF accelerator cavities. The material can achieve higher quality factors, higher temperature operation and potentially higher accelerating gradients compared to conventional niobium. Cornell University has a leading program to produce 2 - 3 micrometer thick coatings of Nb3Sn on Nb for SRF applications using vapor diffusion. This program has been the first to produce quality factors higher than achievable with conventional Nb at usable accelerating gradients. Here we present an update on progress at Cornell University, including studies of the formation of the Nb3Sn layer, density functional theory calculations of Nb3Sn growth, and designs for a sample host cavity for measuring the quench field of Nb3Sn.
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Paper

Title

Page

CBETA, the 4-Turn ERL with SRF and Single Return Loop

635

G.H. Hoffstaetter, N. Banerjee, J. Barley, A.C. Bartnik, I.V. Bazarov, D.C. Burke, J.A. Crittenden, L. Cultrera, J. Dobbins, S.J. Full, F. Furuta, R.E. Gallagher, M. Ge, C.M. Gulliford, B.K. Heltsley, R.P.K. Kaplan, V.O. Kostroun, Y. Li, M. Liepe, W. Lou, C.E. Mayes, J.R. Patterson, P. Quigley, D.M. Sabol, D. Sagan, J. Sears, C.H. Shore, E.N. Smith, K.W. Smolenski, V. Veshcherevich, D. Widger
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.S. Berg, S.J. Brooks, C. Liu, G.J. Mahler, F. Méot, R.J. Michnoff, M.G. Minty, S. Peggs, V. Ptitsyn, T. Roser, P. Thieberger, D. Trbojevic, N. Tsoupas, J.E. Tuozzolo, F.J. Willeke, H. Witte
BNL, Upton, Long Island, New York, USA
D. Douglas
JLab, Newport News, Virginia, USA
J.K. Jones
Cockcroft Institute, Warrington, Cheshire, United Kingdom
D. Jusic
Cornell University, Ithaca, New York, USA
D.J. Kelliher
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
B.C. Kuske, M. McAteer, J. Völker
HZB, Berlin, Germany

Funding: Supported by NSF award DMR-0807731, DOE grant DE-AC02-76SF00515, and NYSERDA.
A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. This technique will be tested in CBETA, which has a single return for the 4-beam energies with strongly-focusing permanent magnets of Halbach type. The high-brightness beam with 150~MeV and up to 40~mA will have applications beyond accelerator research, in industry, in nuclear physics, and in X-ray science. Low current electron beam has already been sent through the most relevant parts of CBETA, from the DC gun through both cryomodules, through one of the 8 similar separator lines, and through one of the 27 similar FFA structures. Further construction is envisioned to lead to a commissioning start for the full system early in 2019.

Slides TUYGBE2 [17.343 MB]

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WEPMF036

RF Test Result of a BNL N-Doped 500 MHz B-Cell Cavity at Cornell

2440

F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
F. Gao, J. Rose
BNL, Upton, Long Island, New York, USA

Cornell's SRF group has collaborated with Brookhaven National Laboratory (BNL) on one 500 MHz CESR type SRF "B-cell" cavity (BNL B-cell) for the National Synchrotron Light Source II. Cornell has been responsible for RF surface preparation, vertical testing, and short cavity string assembly. As a state-of-the-art surface preparation protocol, Cornell selected Nitrogen doping for the BNL B-cell. N-doping has been well demonstrated and established to push the cavity quality factor (Q0) higher in 1.3GHz SRF cavities at many laboratories. Cornell calculated that N-doping could also be beneficial on a 500MHz SRF cavity, with a potential to increase its Q0 by a factor of two compared with the traditional chemical polishing based surface preparation protocol. Here we report on the detailed surface preparation and vertical test result of the BNL B-cell.

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WEPMF037

HF Free Bipolar Electro-Polishing Studies on Niobium SRF Cavities at Cornell With Faraday Technology

2443

F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, P.N. Koufalis, 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, R. Radhakrishnan, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA

Cornell's SRF group and Faraday Technology have been collaborating on two phase-II SBIR projects. One of them is the development and commissioning of a 9-cell scale HF free Bipolar Electro-Polishing (BEP) system. Faraday Technology has upgraded their 1.3 GHz single-cell BEP system for hosting 9-cell cavities. Initial commissioning of the new system was done with a three single-cell cavity string, and high a gradient of 40MV/m was demonstrated during the RF tests at Cornell. After this success with the test string, the 9-cell cavity was processed with the new system at Faraday and RF test was performed at Cornell. Here we report detailed results from these 9-cell scale HF free BEP studies.

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WEPMF038

Microphonics Suppression in the CBETA Linac Cryomodules

2447

SUSPL068

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

N. Banerjee, J. Dobbins, F. Furuta, G.H. Hoffstaetter, R.P.K. Kaplan, 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 New York State Energy Research and Development Agency. The linac cryomodules were constructed with funding from the National Science Foundation.
The Cornell-BNL ERL Test Accelerator (CBETA) is a new multi-turn energy recovery linac currently under construction at Cornell University. It uses two superconducting linacs, both of which are susceptible to microphonics detuning. The high-current injector accelerates electrons to 6 MeV and the main linac accelerates and decelerates electrons by 36 MeV. In this paper, we discuss various measures taken to reduce vibrations caused by instabilities and flow transients in the cryogenic system of the main linac cryomodule. We further describe the use of a Least Mean Square algorithm in establishing a stable Active Microphonics Compensation system for operation of the main linac cavities.

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WEPMF039

Experimental Results on the Field and Frequency Dependence of the Surface Resistance of Niobium Cavities

2451

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

We investigate the field and frequency dependence of the surface resistance of single-cell niobium cavities as a function of surface treatment at 1.3, 2.6, and 3.9 GHz. The surface resistance is broken down into two parts: the temperature-independent residual resistance and the temperature-dependent BCS resistance. While the low-field BCS resistance is known to vary quadratically with frequency, the exact dependence of the BCS and residual resistances on field at higher frequencies are important topics for further investigation. We offer results on a systematic experimental study of the residual and BCS resistance as a function of frequency and field for clean niobium and high-temperature nitrogen-doped niobium.

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WEPMF041

Insights into the Role of C, N, and O Introduced by Low Temperature Baking on Niobium Cavity Performance

2455

SUSPL072

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

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

Previous experiments have shown that introducing nitrogen gas during low temperature bakes (120-160 C) of niobium cavities introduces C, N, and O impurities to the first 10-100 nm of the surface. This new treatment results in higher quality factors and even 'anti-Q-slope' in some cases. However, it is not entirely clear the role that each of these impurities plays in the performance enhancement of the cavities. It has been suggested that interstitial N within the first few nm of the surface is solely responsible for the observed enhancement, but little work has been done on the role of C and O. Because both C and O are abundant in much higher quantities than N near the surface, it is important to understand whether they are beneficial or detrimental to cavity performance. We provide further insight into the effects of C and O on cavity performance by baking in an ambient atmosphere rich in CO2 as opposed to N2.

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WEPMF042

A Computational Method for More Accurate Measurements of the Surface Resistance in SRF Cavities

2458

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

The principal loss mechanism for superconducting RF cavities in normal operation is Ohmic heating due to the microwave surface resistance in the superconducting surface. The typical method for calculating this field-dependent surface resistance R_s(H) from RF measurements of quality factor Q₀ implicitly returns a weighted average of R_s over the surface as a function of peak surface magnetic field H, not the true value of R_s as a function of the local magnitude of H. In this work we present a computational method to convert a measured Q₀ vs. H_peak to a more accurate R_s vs. H_local, given knowledge about cavity geometry and field distribution.

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WEPMF043

Frequency Tuner Development at Cornell for the RAON Half Wave Resonators

2461

M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, 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

The superconducting half-wave-resonators for the RAON project require a slow frequency tuner that can provide at least 80 kHz tuning range. Cornell University has designed, prototyped, and tested a tuner for these half-wave-resonators. In this paper, we present the tuner design, prototype fabrication, test insert preparation, long-term testing and tuner performance test results at cryogenic temperature. The performance of the tuner is analyzed in detail.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF043

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WEPMF044

Updates on the DC Field Dependence Cavity

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

Work at Cornell has demonstrated good agreement between a theoretical model by A. Gurevich of the anti-Q-slope (a field-dependent decrease of the microwave surface resistance) and experimental results from impurity-doped niobium. As a corollary, the model predicts that a strong DC magnetic field applied parallel to the RF surface will produce a similar decrease in surface resistance. In order to explore this prediction for many materials, we have designed a new coaxial cavity with a strong, uniform DC field superimposed over a weak RF field on a removable and replaceable niobium sample. Here we present updates on the progress of this new cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF044

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WEPMF045

Performance of the Prototype SRF Half-Wave-Resonators Tested at Cornell for the RAON Project

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M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, 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

Two prototype superconducting half-wave-resonator (162.5 MHz and β=0.12) for the RAON project have been successfully tested at Cornell University. Detailed vertical performance testing included (1) test of the bare cavity without the helium tank, and (2) test of the dressed cavity with a helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis, showing that the specifications for RAON were met.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF045

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WEPMF046

Modeling of the Frequency and Field Dependence of the Surface Resistance of Impurity-Doped Niobium

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SUSPL073

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

The anti-Q-slope, a field-dependent decrease in surface resistance observed in impurity-doped niobium, has been investigated extensively in 1.3 GHz cavities. New early research into this effect has recently been performed at higher and lower frequencies, revealing an additional dependence on frequency: the anti-Q-slope is stronger at higher frequencies and weaker at lower frequencies. Several models have been proposed to explain the anti-Q-slope, with varying success in this new frequency-dependent regime. In this work, we analyze recent experimental data from a low-temperature-doped 1.3 GHz cavity and a high-temperature nitrogen-doped 2.6 GHz cavity and discuss the implications of these results on the proposed models.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF046

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WEPMF047

Performance of Samples With Novel SRF Materials and Growth Techniques

2475

SUSPL074

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T.E. Oseroff, M. Ge, M. Liepe, J.T. Maniscalco, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
S.R. McNeal
Ultramet, Pacoima, California, USA
M.J. Sowa
Veeco-CNT, Medford, USA

Novel materials are currently being studied in an attempt to push accelerating superconducting RF cavities to support higher accelerating fields and to operate with lower power loss. Growing layers of these materials of the quality necessary has proven to be difficult. In this work, we present the SRF performance of planar samples of the promising materials, NbN and Nb¬3Sn, grown using atomic layer deposition (ALD) and chemical vapor deposition (CVD) respectively. Results are promising.

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WEPMF050

Update on Nb3Sn Progress at Cornell University

2479

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

Niobium-3 Tin (Nb3Sn) is the most promising alternative material for SRF accelerator cavities. The material can achieve higher quality factors, higher temperature operation and potentially higher accelerating gradients compared to conventional niobium. Cornell University has a leading program to produce 2 - 3 micrometer thick coatings of Nb3Sn on Nb for SRF applications using vapor diffusion. This program has been the first to produce quality factors higher than achievable with conventional Nb at usable accelerating gradients. Here we present an update on progress at Cornell University, including studies of the formation of the Nb3Sn layer, density functional theory calculations of Nb3Sn growth, and designs for a sample host cavity for measuring the quench field of Nb3Sn.

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