Recent Advances in High Voltage Electron Beam Injectors

A variety of electron gun systems in the 200 to 500 kV range have been placed into linac service during the past five years. These systems were specifically developed to improve the reliability and performance of high power linear accelerators by providing low emittance pulsed electron beams having highly stable flat-top characteristics. Lifetimes considerably in excesss of 5000 hours have been achieved through the use of low heater power dispenser cathodes, non-intercepting electrodes for control of beam emission and focusing, all-metal and ceramic high temperature brazed dc accelerating columns, and operational vacuum levels of 10-7 to 10-8 Torr. The design features and performance of several of these systems, including short beam pulse and high duty factor are discussed, and typical beam waveforms and equipment photographs are presented.