Measurement of internal dark current in a 17 GHz accelerator structure with an elliptical sidewall
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PhysRevAccelBeams.23.031003.pdf
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Author(s)
Xu, Haoran
Shapiro, Michael A.
Temkin, Richard J.
Date Issued
March 26, 2020
Journal
Physical review. Accelerators and beams
Publisher
American Physical Society
Citation
Xu, Haora, Michael A. Shapiro and Richard J. Temkin. “Measurement of internal dark current in a 17 GHz accelerator structure with an elliptical sidewall”, Physical review. Accelerators and beams, vol. 23, 2020, 031003 © 2020 The Author(s)
Version
Final published version
Abstract
A 17 GHz single cell, standing wave, copper accelerator structure with an axisymmetric elliptical central cell sidewall was tested for internal and downstream dark current as a function of gradient up to 93 MV/m. The elliptical sidewall was predicted to suppress the internal dark current and the lower order multipactor modes as compared with a previously tested structure having a straight sidewall. During the conditioning phase of the elliptical sidewall structure, strong internal dark current generated by an N=1 multipactor mode was observed at gradients in the 10 to 20 MV/m range. After conditioning with 2.2×10^{5} pulses to 93 MV/m, the N=1 mode was completely suppressed and no multipactor resonances were observed. The internal dark current was reduced to a comparatively low level, much smaller than in the previously studied, straight sidewall structure, in good agreement with simulations. The energy spectrum of the electrons colliding with the sidewall was measured using an isolated side dark current monitor and a bias voltage. As the conditioning progressed, the electron energy spectrum showed an increase in the concentration of lower energy electrons, also in good agreement with simulations. Studies of internal dark current may help to understand the rf conditioning and ultimate performance of high gradient accelerator structures.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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Creative Commons Attribution 3.0 unported license
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DOI of Published Version
https://doi.org/10.1103/PhysRevAccelBeams.23.031003
