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Title: Simulation of nonlinear superconducting rf losses derived from characteristic topography of etched and electropolished niobium surfaces

Journal Article · · Physical Review Accelerators and Beams
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A simplified numerical model has been developed to simulate nonlinear superconducting radiofrequency (SRF) losses on Nb surfaces. This study focuses exclusively on excessive surface resistance (Rs) losses due to the microscopic topographical magnetic field enhancements. When the enhanced local surface magnetic field exceeds the superconducting critical transition magnetic field Hc, small volumes of surface material may become normal conducting and increase the effective surface resistance without inducing a quench. We seek to build an improved quantitative characterization of this qualitative model. Using topographic data from typical buffered chemical polish (BCP)- and electropolish (EP)-treated fine grain niobium, we have estimated the resulting field-dependent losses and extrapolated this model to the implications for cavity performance. The model predictions correspond well to the characteristic BCP versus EP high field Q0 performance differences for fine grain niobium. Lastly, we describe the algorithm of the model, its limitations, and the effects of this nonlinear loss contribution on SRF cavity performance.

Research Organization:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Nuclear Physics (NP)
Grant/Contract Number:
AC05-06OR23177
OSTI ID:
1242876
Alternate ID(s):
OSTI ID: 1244079
Report Number(s):
JLAB-ACC-14-1882; DOE/OR/23177-3069; arXiv:1406.7276; PRABFM; 033501
Journal Information:
Physical Review Accelerators and Beams, Vol. 19, Issue 3; ISSN 2469-9888
Publisher:
American Physical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 8 works
Citation information provided by
Web of Science

References (14)

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Enhanced characterization of niobium surface topography journal December 2011
Topographic power spectral density study of the effect of surface treatment processes on niobium for superconducting radio frequency accelerator cavities journal April 2012
Magnetic field enhancement at a pit on the surface of a superconducting accelerating cavity journal July 2015
Negative Surface Free-Energy Effects in Superconducting Niobium journal November 1962
Radio Frequency Magnetic Field Limits of Nb and Nb 3 Sn journal July 2015
Field limit and nano-scale surface topography of superconducting radio-frequency cavity made of extreme type II superconductor journal June 2015
Model for initiation of quality factor degradation at high accelerating fields in superconducting radio-frequency cavities journal November 2010
Thermal stabilities and optimal operating parameters for the Oak Ridge Spallation Neutron Source superconducting linear accelerator journal March 2007
Exact and numerical solutions to a Stefan problem with two moving boundaries journal January 2008
Evidence for non-linear BCS resistance in SRF cavities journal July 2006
Kapitza conductance and thermal conductivity of copper niobium and aluminium in the range from 1.3 to 2.1 K journal February 1973
Characterization of Nb SRF cavity materials by white light interferometry and replica techniques journal June 2013
Routine characterization of 3D profiles of SRF cavity defects using replica techniques journal December 2010

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