Matsumoto, H.

Paper	Title	Page
MOP76	Ultra-High-Vacuum Problem for 200 keV Polarized Electron Gun with NEA-GaAs Photocathode	201
	T. Nakanishi, F. Furuta, M. Kuwahara, K. Naniwa, S. Okumi, M. Yamamoto, N. Yamamoto, K. Yasui DOP Nagoya, Nagoya H. Kobayakawa, Y. Takashima DOE Nagoya, Nagoya-City M. Kuriki, H. Matsumoto, M. Yoshioka KEK, Ibaraki
	For a polarized electron source based on photoemission from GaAs, a NEA (Negative Electron Affinity) surface makes an indispensable role to extract polarized electrons in conduction band into vacuum. The NEA surface is also considered as a best surface to provide a beam with a minimum initial beam-emittance. However, the NEA surface state is realized by a mono-layer of electric dipole moment (that is Ga(-)-Cs(+)) formed at the surface and thus it is easily degraded by desorption of harmful residual gas, desorption of harmful gas created by field emission from HV-cathodes and ion back-bombardment. In order to reduce the effects of (a) and (c), extremely good UHV is required. Presently total pressure of 4·10-12 torr and respective partial pressures of 3·10-13 torr and 4·10-13 torr for H2O and CO2 were achieved at our gun chamber. Field emission dark current must be extremely suppressed to reduce the effect of (c). The maximum field gradient of 7.8 MV/m is applied for electrode envelope (3.0 MV/m for cathode surface) at 200 kV DC bias-voltage, but total dark current was suppressed below 1 nA for our electrodes. The NEA lifetime under these conditions will be reported at the conference.
TU201	The KEK C-Band RF System for a Linear Collider	256
	H. Matsumoto, S. Takeda, S.S. Win, M. Yoshida KEK, Ibaraki H. Baba, T. Shintake RIKEN Spring-8 Harima, Hyogo J-O. Oh PAL, Pohang
	The C-band (5712 MHz) main linac has been developed just motivated by the urgent and essential physics program at the e+e- linear collider. In total ~8000 accelerating structures and ~4000 klystrons with modulators are needed for 500 GeV C.M. energy. Therefore these units have to meet strict requirements for: high reliability, simplicity, easy operation, reasonable power efficiency and low cost. This list provides a guiding principle and the boundary conditions for our design work. We have already developed the conventional and PPM type 50 MW class C-band klystrons, modulators, and HOM-free accelerator structures. The first high power an rf compressor cavity made of a low thermal expansion material was designed to provide stable operation even with a very high Q of 200 k, it was successfully operated an output rf power of 135 MW at KEK. The C-band linac rf-system will be used for the SASE-FEL project at SPring-8, but it will also serve to verify the design and components, which can eventually be deployed for the main linac rf system in a future linear collider.
	Transparencies
TU202	Low Emittance 500 kV Thermionic Electron Gun	261
	K. Togawa, H. Baba, T. Inagaki, K. Onoe, T. Shintake, T. Tanaka RIKEN Spring-8 Harima, Hyogo H. Matsumoto KEK, Ibaraki
	A 500 kV pulsed electron gun has been constructed for the injector system of the SASE-FEL project at SPring-8 (SCSS project). A CeB6 single crystal was chosen as a thermionic cathode, because of its excellent emission properties. We have succeeded in generating a 500 keV beam with 1 A peak current and 3 μs FWHM. The beam was very stable with low jitter. The beam emittance has been measured by means of double-slits method, and the normalized rms emittance of 1.1 π·mm·mrad has been obtained. We report on the experimental result on the emittance measurement of the CeB6 electron gun.
	Transparencies
THP23	An Electrode With Molybdenum-Cathode and Titanium-Anode to Minimize Field Emission Dark Currents	645
	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
	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.