SRF2017 - List of Authors (Gurevich, A.V.)

Paper

Title

Page

Cryogenic Probe Station at Old Dominion University Center for Accelerator Science

128

J. Makita, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
G. Ciovati
JLab, Newport News, Virginia, USA

With a growing effort in research and development of an alternative material to bulk Nb for a superconducting radiofrequency (SRF) cavity, it is important to have a cost effective method to benchmark new materials of choice. At Old Dominion University's Center for Accelerator Science, a cryogenic probe station (CPS) will be used to measure the response of superconductor samples under RF fields. The setup consists of a closed-cycle refrigerator for cooling a sample wafer to a cryogenic temperature, a superconducting magnet providing a field parallel to the sample, and DC probes in addition to RF probes. The RF probes will extract a quality factor from a sample patterned in a coplanar waveguide resonator structure on a 2' wafer. From the measured quality factor, the surface resistance and the penetration depth as a function of temperature and magnetic field will be calculated. This paper will discuss the design and measurement procedures of the current CPS setup.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB035

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TUXBA04

A Unified Theory of Surface Resistance and the Residual Resistance of SRF Cavities at Low Temperatures

T. Kubo
KEK, Ibaraki, Japan
A.V. Gurevich
ODU, Norfolk, Virginia, USA

The Mattis-Bardeen (MB) theory has been widely used for the calculation of the surface resistance of superconductors at weak RF fields. It is well known that the observed surface resistance decreases exponentially as the temperature decreases but tends to a constant residual resistance which is not described by the MB theory. Using the quasiclassical formalism of the microscopic BCS theory, we have developed a unified theory of the surface resistance which, in addition to the MB contribution, includes the residual resistance. Based on this theory, possible materials treatments to reduce the surface resistance are discussed.

Slides TUXBA04 [2.207 MB]

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WEXA08

Current-blocking Grain Boundaries in SRF Cavities and RF Dissipation Due to Nonlinear Dynamics of Josephson Vortices under Strong RF Fields

A.V. Gurevich, A. Sheikhzada
ODU, Norfolk, Virginia, USA

Funding: Work supported by US DOE under grant # 100387-020
Grain boundaries (GBs) in polycrystalline Nb cavities do not significantly degrade the SRF performance. However, the situation may change for Nb3Sn in which GBs can partially obstruct current and pin vortices, as it has been established in many previous studies. Such weak-linked GBs can cause a medium-field Q slope and cavity quench triggered by guided penetration of vortices along networks of GBs. Vortices trapped at GBs can also contribute to the residual surface resistance. This talk gives an overview of current-limiting mechanisms of GBs and dissipation of vortices in strongly-coupled GBs under RF field. We present results of extensive numerical simulations of vortices in GBs in polycrystalline bulk and thin films, and contribution of vortices to the RF dissipation. Our simulations revealed Cherenkov instability of Josephson vortices driven by strong RF currents and generation of vortex-antivortex pairs, dynamic transition of vortices into phase slips in thin films, and dynamic interaction of moving vortices with pinning centers. Contributions of these mechanisms to the field dependent surface resistance and reduction of the RF breakdown field is discussed.

Slides WEXA08 [9.505 MB]

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Paper	Title	Page
MOPB035	Cryogenic Probe Station at Old Dominion University Center for Accelerator Science	128
	J. Makita, J.R. Delayen, A.V. Gurevich ODU, Norfolk, Virginia, USA G. Ciovati JLab, Newport News, Virginia, USA
	With a growing effort in research and development of an alternative material to bulk Nb for a superconducting radiofrequency (SRF) cavity, it is important to have a cost effective method to benchmark new materials of choice. At Old Dominion University's Center for Accelerator Science, a cryogenic probe station (CPS) will be used to measure the response of superconductor samples under RF fields. The setup consists of a closed-cycle refrigerator for cooling a sample wafer to a cryogenic temperature, a superconducting magnet providing a field parallel to the sample, and DC probes in addition to RF probes. The RF probes will extract a quality factor from a sample patterned in a coplanar waveguide resonator structure on a 2' wafer. From the measured quality factor, the surface resistance and the penetration depth as a function of temperature and magnetic field will be calculated. This paper will discuss the design and measurement procedures of the current CPS setup.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB035
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUXBA04	A Unified Theory of Surface Resistance and the Residual Resistance of SRF Cavities at Low Temperatures
	T. Kubo KEK, Ibaraki, Japan A.V. Gurevich ODU, Norfolk, Virginia, USA
	The Mattis-Bardeen (MB) theory has been widely used for the calculation of the surface resistance of superconductors at weak RF fields. It is well known that the observed surface resistance decreases exponentially as the temperature decreases but tends to a constant residual resistance which is not described by the MB theory. Using the quasiclassical formalism of the microscopic BCS theory, we have developed a unified theory of the surface resistance which, in addition to the MB contribution, includes the residual resistance. Based on this theory, possible materials treatments to reduce the surface resistance are discussed.
	Slides TUXBA04 [2.207 MB]
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEXA08	Current-blocking Grain Boundaries in SRF Cavities and RF Dissipation Due to Nonlinear Dynamics of Josephson Vortices under Strong RF Fields
	A.V. Gurevich, A. Sheikhzada ODU, Norfolk, Virginia, USA
	Funding: Work supported by US DOE under grant # 100387-020 Grain boundaries (GBs) in polycrystalline Nb cavities do not significantly degrade the SRF performance. However, the situation may change for Nb3Sn in which GBs can partially obstruct current and pin vortices, as it has been established in many previous studies. Such weak-linked GBs can cause a medium-field Q slope and cavity quench triggered by guided penetration of vortices along networks of GBs. Vortices trapped at GBs can also contribute to the residual surface resistance. This talk gives an overview of current-limiting mechanisms of GBs and dissipation of vortices in strongly-coupled GBs under RF field. We present results of extensive numerical simulations of vortices in GBs in polycrystalline bulk and thin films, and contribution of vortices to the RF dissipation. Our simulations revealed Cherenkov instability of Josephson vortices driven by strong RF currents and generation of vortex-antivortex pairs, dynamic transition of vortices into phase slips in thin films, and dynamic interaction of moving vortices with pinning centers. Contributions of these mechanisms to the field dependent surface resistance and reduction of the RF breakdown field is discussed.
	Slides WEXA08 [9.505 MB]
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)