Compact reflex triode operation at 10 Hz repetition rate and long pulsewidths

Abstract

This study focuses on the performance of a bimodal carbon fiber (CF) cathode and a carbon-epoxy multicapillary (CEM) cathode with microwaves at 50kV/m at 2m lasting 100 ns in a compact reflex triode virtual cathode oscillator (vircator). It was previously revealed that the CEM cathode was able to produce uniform emission distribution for a long duration1. To further uncover the location(s) where plasma is forming, an intensified CCD camera is used to image both cathodes with high spatial and temporal resolution. A titanium grade 1 (TiG1) anode that is 70% transparent is used to minimize outgassing in the system resulting in the cathode being the primary outgassing constituent2. One data set for each cathode was taken. Each data set contains diode current, voltage, and microwave fields over the course of 10,000 shots. A performance baseline is shown by comparing the evolution of these data over the course of the experiments. An 8 stage, 168 J pulse forming network (PFN) based Marx generator serves to drive both cathodes at 250 kV, 4 kA with ∼175 ns pulsewidth, achieving current densities of ∼200 A/cm3. The operating frequency of interest is set in the range of 1–2 GHz, where the tunability is achieved by varying the size of the anode-cathode (A-K) gap. In all experiments the gap is fired at a 10 Hz pulse repetition rate. The characteristics of one type of cathode over the other, depending on the operating conditions, are discussed in detail.