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 μs. 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 (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.