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Title: Measurement of internal dark current in a 17 GHz, high gradient accelerator structure

Abstract

We report the measurement of the internal dark current in a 17 GHz, high gradient accelerator cavity and its comparison with theory. The cavities were fabricated from copper and had a sidewall that was either uncoated or coated with diamondlike carbon or TiN. The dark current was monitored by a downstream detector and by detectors behind two small slits made in the cavity sidewall. With an increasing gradient, the downstream current increased monotonically, as expected for field emission. The variation of the internal, side dark current was not monotonic but showed the onset of peaks at gradients near 45 and 65 MV / m . These were identified as the N = 2 and N = 1 single point multipactor resonances. The total internal dark current was estimated at ~ 15 30 A . The magnitude of the internal dark current and its dependence on the gradient were in good agreement with simulations using the cst code as well as an in-house code. Processing to a higher gradient, ~ 90 MV / m , eliminated the N = 2 mode, but the N = 1 mode persisted. The coated sidewall cavities showed the same multipactor resonances as the uncoated structure. However, at the highest gradient achieved in testing, the coated structures showed a modest reduction in the internal dark current.

Authors:
; ;
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1493656
Alternate Identifier(s):
OSTI ID: 1612297
Grant/Contract Number:  
SC0015566
Resource Type:
Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Name: Physical Review Accelerators and Beams Journal Volume: 22 Journal Issue: 2; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; Physics

Citation Formats

Xu, H., Shapiro, M. A., and Temkin, R. J. Measurement of internal dark current in a 17 GHz, high gradient accelerator structure. United States: N. p., 2019. Web. doi:10.1103/PhysRevAccelBeams.22.021002.
Xu, H., Shapiro, M. A., & Temkin, R. J. Measurement of internal dark current in a 17 GHz, high gradient accelerator structure. United States. doi:10.1103/PhysRevAccelBeams.22.021002.
Xu, H., Shapiro, M. A., and Temkin, R. J. Wed . "Measurement of internal dark current in a 17 GHz, high gradient accelerator structure". United States. doi:10.1103/PhysRevAccelBeams.22.021002.
@article{osti_1493656,
title = {Measurement of internal dark current in a 17 GHz, high gradient accelerator structure},
author = {Xu, H. and Shapiro, M. A. and Temkin, R. J.},
abstractNote = {We report the measurement of the internal dark current in a 17 GHz, high gradient accelerator cavity and its comparison with theory. The cavities were fabricated from copper and had a sidewall that was either uncoated or coated with diamondlike carbon or TiN. The dark current was monitored by a downstream detector and by detectors behind two small slits made in the cavity sidewall. With an increasing gradient, the downstream current increased monotonically, as expected for field emission. The variation of the internal, side dark current was not monotonic but showed the onset of peaks at gradients near 45 and 65 MV/m. These were identified as the N=2 and N=1 single point multipactor resonances. The total internal dark current was estimated at ~15–30 A. The magnitude of the internal dark current and its dependence on the gradient were in good agreement with simulations using the cst code as well as an in-house code. Processing to a higher gradient, ~90 MV/m, eliminated the N=2 mode, but the N=1 mode persisted. The coated sidewall cavities showed the same multipactor resonances as the uncoated structure. However, at the highest gradient achieved in testing, the coated structures showed a modest reduction in the internal dark current.},
doi = {10.1103/PhysRevAccelBeams.22.021002},
journal = {Physical Review Accelerators and Beams},
number = 2,
volume = 22,
place = {United States},
year = {2019},
month = {2}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1103/PhysRevAccelBeams.22.021002

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Cited by: 1 work
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