High-current density electron beam generation from a polymer velvet cathode.

Intense electron beam generation studies were carried out using polymer velvet as a cathode material. The typical electron beam parameters were 250 kV, 15 kA, 100 ns, with a few hundred A cm[?]2 current density. The cathode plasma expansion velocity and the effective initial emission area have been calculated using the perveance data. It was found that the gap closure velocity and the initial emission areas vary randomly on a shot-to-shot basis. In comparison with a graphite cathode, the gap closure velocity of the velvet cathode is less for lower diode gaps, but is much higher for the larger accelerating gaps. One-way analysis of variance was employed to examine the statistical correlation between the diode voltage, current, plasma velocity and the effective emission area for various diode gaps and for two different cathode materials. It was shown that the mean diode voltage, current, plasma velocity and the effective emission area are different for graphite and velvet cathodes whereas the statistical variations of diode voltage and plasma expansion velocities are not cathode material dependent. However, the mean effective emission area is cathode material dependent as are the variances. [ABSTRACT FROM AUTHOR]