Performances of Velvet Cathodes With Different Geometries in a Reflex Triode Vircator

A frequency tunable vircator, which has the reflex triode geometry, was designed and experimentally tested. The cloth velvet was used as the cathode material. The planar and the Ernst-profiled velvet cathodes, which have diameters of 40, 50, 60, and 70 mm, were used in the experiments. The electric field strength values and the corresponding frequencies of the radiated microwave were measured and analyzed for each of the cathodes. The anode-cathode distances between 4 and 16 mm were swept in the experiments. The planar cathodes display larger electric field strength values, whereas the Ernst-profiled cathodes have wider frequency ranges. The characteristics of the velvet, such as tuft density and fiber dimensions, were investigated in detail using scanning electron microscope images. The condition of the vacuum was also observed during shots.