Two Dimensional PIC Simulation of Anode Foil Evolution in Axially-Extracted Vircator

Summary form only given. We have performed two-dimensional, relativistic, electromagnetic particle-in-cell simulation of foil evolution in a virtual cathode oscillator (vircator). These simulation have been done using a locally modified form of Xoopic code. The modified code has been validated using two vircator designs available from the literature, with considerable differences in their parameters. Our earlier simulations showed that the model used for the anode foil significantly affects system performance. In the earlier simulations, we assumed that the foil transparency remains constant in time. That leads to three errors. Firstly, it eliminates the major closure mechanism in the diode. Secondly, since the foil ablates in time, its transparency should be time-dependent. Thirdly, the plasma created by foil ablation significantly affects vircator dynamics, which is ignored in our earlier model. These issues are of particular importance in long-pulse vircators. Our study is divided into two parts. The first part involves a study of foil damage with time, and the consequent plasma generation and expansion. On the basis of this model, we attempt to estimate the closure time of the diode, plasma expansion time and the lifetime of the foil. And second part involve the effect of plasma expansion on the performance. We compare the results, such as output frequency and power, from simulations both with and without ablation effects. We find a considerable difference. Detailed results are presented in the paper.