Experimental results of a high power rep-rate velvet cathode

The primary goal of the Electromagnetic Sources Division of the Advanced Weapons and Survivability Directorate at the Phillips Laboratory is the development of high power microwave (HPM) devices for a variety of Air Force Applications. Recent interest has been in the repetition-rate (rep-rate) operation of traditionally single-shot HPM sources. Integral to this development is an understanding of the operation of velvet cathodes at multi-gigawatt power levels under rep-rate conditions. Velvet has been shown to emit very uniformly at relatively low field levels (<30 kV/cm), but suffers from the problem of outgassing during the beam pulse. This outgassing could cause the diode to short in subsequent pulses or a voltage breakdown in other areas of the microwave tube due to the increased pressure. Initial tests have been performed to determine the feasibility of the application of velvet cathodes for rep-rate operation. These tests were performed on the Phillips Laboratory Rep-Rate Pulser, a 5 /spl Omega/, variable voltage, rep-rate device. This pulser can deliver 150-500 kV, 500 ns pulses to a 5 /spl Omega/ load at a rep-rate of a few Hz depending on the operating voltage. The temporal evolution of the pressure within the tube as a function of voltage was monitored during the tests to determine the maximum rep-rate dictated by the velvet cathode. The results of these experiments are given in this paper.