Plasma sources for high-current electron beam generation

A review of experimental studies of the operation of cathodes made of metal -ceramic, velvet, corduroy, carbon fibers, carbon fabric, and different typ es of ferroelectrics is presented. These cathodes operated at electric fiel ds 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-con stant diode impedance. All cathodes had the same diameter and were tested i n a diode powered by a high-voltage generator (300 kV, 85 Omega, 250 ns, le ss than or equal to5 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 di scharges. Different types of electrical and optical diagnostics were used t o study the formation and parameters of the plasma, the potential distribut ion 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 the ir compatibility with vacuum requirements are presented as well. (C) 2001 A merican Institute of Physics.