Photocathode emission studies: Dark current and Schottky-enabled photo-electrons in a high-field RF gun
- Dept. of Eng. Phys., Tsinghua U. (China)
- Switzerland
We report on dark current and Schottky-enabled photoemission from a copper photocathode surface. Field-emitted dark current is a major gradient-limiting factor in RF cavities. Field emission is generally attributed to geometrical projections on the bulk surface whose field enhancement factor ({beta}) and the emitting area (A{sub e}) can be extracted from the Fowler-Nordheim (FN) plot. Measurements were made at Tsinghua S-band RF gun facility in two separate experiments. Using the traditional FN formula for RF fields we discovered that field enhancement factor ({beta}) alone cannot explain the full data set. Instead, we found that a low work function at some sites is required. In addition, surface analysis of the cathode after the experiment shows that geometric {beta} indicated would be < 10. Thus we conclude that low work function sites with a small {beta} are responsible for dark current emission and subsequent breakdown in high-gradient structures. The origin of these sites is unclear but could be due to defects or impurities.
- OSTI ID:
- 22075869
- Journal Information:
- AIP Conference Proceedings, Vol. 1507, Issue 1; Conference: 15. advanced accelerator concepts workshop, Austin, TX (United States), 10-15 Jun 2012; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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