Plasma sources for high-current electron beam generation

Abstract

A review of experimental studies of the operation of cathodes made of metal-ceramic, velvet, corduroy, carbon fibers, carbon fabric, and different types of ferroelectrics is presented. These cathodes operated at electric fields in the range of 5–60 kV/cm that allowed the generation of electron beams with duration of several hundreds of nanoseconds while keeping a quasi-constant diode impedance. All cathodes had the same diameter and were tested in a diode powered by a high-voltage generator (300 kV, 85 Ω, 250 ns, ⩽5 Hz). It was shown that the source of electrons for all the studied cathodes is a plasma which is formed as a result of surface discharges. Different types of electrical and optical diagnostics were used to study the formation and parameters of the plasma, the potential distribution inside the anode–cathode gap, and the uniformity and divergence of the extracted electron beam as a function of the amplitude and rise time of the accelerating pulse. Results of the lifetime of the tested cathodes and their compatibility with vacuum requirements are presented as well.