Sanghyun Park (SLAC)
In light of the SPEAR3 upgrade where the goal is to store up to 500 mA of beam current at 3.0 GeV beam energy, the injector RF gun and linac performance must be optimized in terms of relia-bility and injection rate. The basic layout of the system remains unchanged for the last ten years of operation. The 1.5-cell standing wave thermionic RF gun is the source of the bunched beam at 10 pulses per second. An alpha magnet compresses the bunches to a few picoseconds, and a traveling-wave beam chopper then allows only three or four bunches to reach the linac near the end of the RF pulse. This way the beam loading to the linac is minimized and the linac beam to the Booster synchrotron reaches the maximum beam energy. Over the past few years some improvements were made to achieve the system reliability and stability. The original klystrons were replaced by one high-power tube. The modulator is now charged by a switching power supply. The drive amplifier that feeds the klystron RF input was based on thermionic triodes, but it is solid-state now. The fabrication of the gun cathode assembly underwent several cycles of iteration. One or more of feedback control was employed to stabilize the linac beam energy when needed. In this paper we will describe the modifications mentioned above, the present status, and the plans for the future.
 R. Hettel, et al., 'SPEAR3 - A Low Emittance Source for SSRL,' PAC99 Proc.
 J.N. Weaver, et al., 'The Linac and Booster RF Systems for a Dedicated Injector for SPEAR,' PAC91 Proc.
 S. Park, 'RF Power Distribution and Phasing at SSRL Injector Linac,' Linac98 Proc.
* Work supported at SLAC under U.S. DoE contract DE-AC03-76SF00515
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