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- T. Nakanishi, F. Furuta, T. Gotou, M. Kuwahara, K. Naniwa, S. Okumi, M. Yamamoto, N. Yamamoto, K. Yasui
DOP Nagoya, Nagoya
- H. Matsumoto, M. Yoshioka
KEK, Ibaraki
- K. Togawa
RIKEN Spring-8 Harima, Hyogo
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A systematic study to minimize field emission dark currents from high voltage DC electrode has been continued. It is clearly demonstrated that much lower field emissions observed for Molybdenum (Mo) and Titanium (Ti) in comparison to Stainless-steel and Copper. Furthermore, by analyzing gap-length dependence data of the dark current from Mo and Ti, we can find a method to separate the primary field emission currents (FEC) from secondary induced currents (SIC). The latter currents will be created by possible bombardments of metal surface of anode or cathode by electrons or positive ions, respectively. From this data analysis, it is suggested that Mo is suitable for cathode due to its smallest FEC, and Ti is adequate for anode due to relatively small SIC. This prediction was confirmed by our experiment using a pair of Mo and Ti electrode, which showed the total dark current is suppressed below 1 nA at 105 MV/m applied for an area of 7 mm2 with a gap-length of 1.0 mm. Therefore this Mo-Ti electrode seems useful for a high field gradient DC gun, especially for a GaAs-photocathode gun using an NEA (Negative Electron Affinity) surface.
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