The Spear Injector Rf Gun and Linac Performace*

In light of the SPEAR3 upgrade project 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 optimised in terms of reliability and injection rate. The basic linac system layout has not been changed for the last ten years of operation. A thermionic1.5-cell standing wave RF gun is the source of bunched beams at 10 Hz. An alpha magnet then compresses the bunch length to a few picosecond, and a travelling-wave beam chopper then allows only 3 or 4 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 energy. Some improvements were made over the past few years to achieve the system reliability and stability. The original three klystrons were replaced by one high-power tube. The modulator is presently charged by a switching power supply. The drive amplifier feeding the klystron was based on thermionic triodes; it is a solid-state amplifier now. The gun cathode assembly underwent several iterations. Some feedback controls stabilise the linac beam energy as needed. In this paper we describe the modifications mentioned above, the present status, and the plans for the future.