Simulation of a Distributed Cathode in a Linear-Format Crossed-Field Amplifier

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The effects of a distributed cathode in a linear-format crossed-field amplifier are simulated in VSim and analyzed. A linear-format, injected-beam, 150-MHz, low-power (~100 W), moderate-gain (7 dB), meander-line crossed-field amplifier (CFA) designed and tested at Northeastern University is used as the basis for the simulation model. The simulation results were validated by the experimental results from that CFA. The injected-beam model was then replaced with a distributed cathode requiring electron injection with an energy below the sole electrode. A new method, which uses a divergence-free region, was developed to simulate this distributed cathode. This model was validated and studied using three different current injection profiles. The distributed cathode offered no improvements to gain or the signal-to-noise ratio (SNR). Increasing the cathode area lowers the noise but is counteracted by the corresponding decrease in gain. The limits to the gain in this particular device are due to the current space charge limit for the higher power operation and the SNR for the lower power operation.