High current, low pressure plasma cathode electron gun

A plasma-cathode electron gun based on a moderate pressure (> 5 mTorr) cold-cathode discharge and a high perveance, multiaperture accelerator was previously developed at Hughes Research Laboratories and produced electron beam currents of up to 1 kA at voltages of over 200 kV for pulse lengths of 100 mu s. This gun was limited in pulse repetition frequency and duty by the gas-puff system that provided adequate gas pressure in the hollow cathode to operate the glow discharge while keeping the pressure in the beam transport region sufficiently low. We describe a new plasma cathode electron gun (PCE gun) that eliminates this problem by replacing the glow-discharge plasma generator in the electron gun by a low-pressure thermionic discharge in a magnetic multipole confinement chamber. Proper design of the plasma generator and electrical circuit provides high electron-current densities to the accelerator structure at very low gas pressure (< 10(-4) Torr). The static gas pressure permits the pulse repetition frequency to be very high (> 1.5 kHz demonstrated) with electron beam currents up to 200 A at voltages up to 120 kV demonstrated. The design and performance of the PCE gun, along with several models used to predict and scale the performance, are discussed. (C) 2000 American Institute of Physics. [S0034-6748(00)05302-8].