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Title: rf losses in a high gradient cryogenic copper cavity

The development of high brightness electron sources can enable an increase in performance and reduction in size of extreme X-ray sources such as free electron lasers (FELs). A promising path to high brightness is through larger electric fields in radio-frequency (rf) photoinjectors. Recent experiments with 11.4 GHz copper accelerating cavities at cryogenic temperatures have demonstrated 500 MV / m surface electric fields with low rf breakdown rates. However, when the surface electric fields are larger than 300 MV / m, the measured cavity quality factor, Q 0, decreases during the input rf pulse by up to 30%, recovering before the next rf pulse. Here, we present an experimental study of the rf losses, manifested as degradation of Q 0, in a copper cavity operated at cryogenic temperatures and high gradients. The experimental conditions range from temperatures of 10–77 K and rf pulse lengths of 100–800 ns, using surface electric fields up to 400 MV / m. We developed a model for the change in Q 0 using measured field emission currents and rf signals. We find that the Q 0 degradation is consistent with the rf power being absorbed by strong field emission currents accelerated inside the cavity.
Authors:
 [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [2]
  1. Univ. of California, Los Angeles, CA (United States)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
PHY-1549132; AC02-76-SF00515
Type:
Accepted Manuscript
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Volume: 21; Journal Issue: 6; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; cryogenic technology; room temperature RF
OSTI Identifier:
1461825