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Title: Dependence of trapped-flux-induced surface resistance of a large-grain Nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown through Tc

Recent studies by Romanenko et al. revealed that cooling down a superconducting cavity under a large spatial temperature gradient decreases the amount of trapped flux and leads to reduction of the residual surface resistance. In the present paper, the flux expulsion ratio and the trapped-flux-induced surface resistance of a large-grain cavity cooled down under a spatial temperature gradient up to 80K/m are studied under various applied magnetic fields from 5E-6 T to 2E-5 T. We show the flux expulsion ratio improves as the spatial temperature gradient increases, independent of the applied magnetic field: our results supports and enforces the previous studies. We then analyze all RF measurement results obtained under different applied magnetic fields together by plotting the trapped- flux-induced surface resistance normalized by the applied magnetic field as a function of the spatial temperature gradient. All the data can be fitted by a single curve, which defines an empirical formula for the trapped- flux-induced surface resistance as a function of the spatial temperature gradient and applied magnetic field. The formula can fit not only the present results but also those obtained by Romanenko et al. previously. Furthermore, the sensitivity rfl of surface resistance from trapped magnetic flux of fine-grainmore » and large-grain niobium cavities and the origin of dT/ds dependence of Rfl/Ba are also discussed.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Chinese Academy of Sciences (CAS), Lanzhou (China); Univ. of Chinese Academy of Science, Beijing (China); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
  2. High Energy Accelerator Organization, Ibaraki (Japan); SOKENDAI (the Graduate Univ. for Advanced Studies), Kanagawa (Japan)
  3. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Publication Date:
OSTI Identifier:
1307796
Report Number(s):
JLAB-ACC-16-2349; DOE/OR/23177-3930
Journal ID: ISSN 2469-9888; PRABFM
Grant/Contract Number:
AC05-06OR23177; 26800157; 26600142
Type:
Published Article
Journal Name:
Physical Review Accelerators and Beams (Online)
Additional Journal Information:
Journal Name: Physical Review Accelerators and Beams (Online); Journal Volume: 19; Journal Issue: 8; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS