Influence of anode plasma on high-power microwave generation in virtual cathode oscillator

Summary form only given. Anode plasma formation in virtual cathode oscillator (vircator) is unavoidable because of the striking and heating of anode by intense electron beam, which affects important vircator physics issues especially the generation of high- power microwave (HPM). By theoretical and simulation methods, it is found that energy deposition which may cause serious temperature rise in anode surfaces, followed by thermal desorption and ionization dominates the formation of anode plasma in vircator. The expansion velocity of anode plasma layers is about several centimeters per microsecond,1 but the positive ions in the outmost layer may drift much faster towards cathode with a velocity of several hundred centimeters per microsecond by theoretical and simulation methods, which also cause obvious influence on vircator output. Formation and expansion of high density anode plasma cause diode closure and HPM radiation breakdown in vircator. Simulation results show that the diode impedance, beam-wave efficiency and microwave frequency will all decrease when the density of anode plasma increases in some high range, meanwhile the pulse-shortening will be more obvious and the spectrum become worse. Such effects will be greater while the average nucleon number of positive ions in anode plasma is larger.