Initial performance of a 500 kV chopper prebuncher injection system for a 17 GHz linac

The design features of a 17 GHz chopper prebuncher injection system are described, and initial test results operating with a 500 kV low emittance electron gun and single section 17 GHz linac are presented. The 17 GHz traveling wave relativistic klystron that provides the RF power to the linac structure, and the 500 W electron gun that forms the low emittance (βγε = 3π mm-mradian) source for the injection system, are pulsed simultaneously using the MIT Plasma Science and Fusion Center HV modulator. The HV injection system is designed to produce RF bunches of 15° to 20° for injection into the linac structure, with subsequent compression to approximately 1 degree to provide sub-picosecond bunch operation over an energy range of 10 to 20 MeV with steady-state pulse currents of up to 250 mA. The use of an economical, on-line diagnostic system having the capability of accurately measuring the short RF bunch performance of the 17 GHz linac would be highly advantageous; and a simple technique of accomplishing this, using higher order mode 17 GHz cavities, is discussed