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Title: Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

In niobium superconducting radio frequency (SRF) cavities for particle acceleration, a decrease of the quality factor at lower fields—a so-called low field Q slope or LFQS—has been a long-standing unexplained effect. By extending the high Q measurement techniques to ultralow fields, we discover two previously unknown features of the effect: (i) saturation at rf fields lower than E acc~0.1 MV/m; (ii) strong degradation enhancement by growing thicker niobium pentoxide. Our findings suggest that the LFQS may be caused by the two level systems in the natural niobium oxide on the inner cavity surface, thereby identifying a new source of residual resistance and providing guidance for potential nonaccelerator low-field applications of SRF cavities.
Authors:
 [1] ;  [2]
  1. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  2. Univ. of Chicago, IL (United States).The James Franck Institute and Department of Physics
Publication Date:
Report Number(s):
FERMILAB-PUB-17-269-TD; arXiv:1705.05982
Journal ID: ISSN 0031-9007; PRLTAO; 1600003
Grant/Contract Number:
AC02-07CH11359
Type:
Published Article
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 119; Journal Issue: 26; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS
OSTI Identifier:
1415053
Alternate Identifier(s):
OSTI ID: 1454719

Romanenko, A., and Schuster, D. I.. Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes. United States: N. p., Web. doi:10.1103/PhysRevLett.119.264801.
Romanenko, A., & Schuster, D. I.. Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes. United States. doi:10.1103/PhysRevLett.119.264801.
Romanenko, A., and Schuster, D. I.. 2017. "Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes". United States. doi:10.1103/PhysRevLett.119.264801.
@article{osti_1415053,
title = {Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes},
author = {Romanenko, A. and Schuster, D. I.},
abstractNote = {In niobium superconducting radio frequency (SRF) cavities for particle acceleration, a decrease of the quality factor at lower fields—a so-called low field Q slope or LFQS—has been a long-standing unexplained effect. By extending the high Q measurement techniques to ultralow fields, we discover two previously unknown features of the effect: (i) saturation at rf fields lower than Eacc~0.1 MV/m; (ii) strong degradation enhancement by growing thicker niobium pentoxide. Our findings suggest that the LFQS may be caused by the two level systems in the natural niobium oxide on the inner cavity surface, thereby identifying a new source of residual resistance and providing guidance for potential nonaccelerator low-field applications of SRF cavities.},
doi = {10.1103/PhysRevLett.119.264801},
journal = {Physical Review Letters},
number = 26,
volume = 119,
place = {United States},
year = {2017},
month = {12}
}