Characterization of Cesium Iodide-Coated Carbon-Fiber Aluminum Cathode for an $S$ -Band High-Efficiency Vircator

Carbon-fiber-aluminum (CFA) cathode is characterized to generate high-power microwave (HPM) from a high-efficiency three-cavity virtual-cathode oscillator (vircator). Plasma expansion velocity associated with the cesium iodide (CsI)-coated CFA cathode is determined in the experiment. It is found that the stationary plasma expansion velocity is diminished by CsI-coating to about 3 ${\mathrm {cm}}/\mu \text{s}$ when driving by a 300-kV electrical pulse. Particle-in-cell (PIC) simulations indicate that the proposed vircator is capable of generating 550-MW $S$ -band HPM at a central frequency of 2.1 GHz, when the diode voltage and current are 420 kV and 9.2 kA, respectively. The corresponding power conversion efficiency is as high as 14%. The generated HPM is with the TE 10 mode of rectangular waveguide, which can give rise to an on-axis radiation pattern without requiring mode converter.