Effects of diode current on high power microwave generation in a vircator

An experiment of a virtual cathode oscillator (vircator) built on the low impedance intense electron beam accelerator Flash II is reported. A novel spectrum diagnosis method-a, circulating dispersion line-is proposed. A thin oil layer coated graphite cathode is introduced in be experiment to decrease the delay Mine of the explosive emission process and obtain a homogeneous electron beam emission for improving the high-power microwave (HPM) generation efficiency. The effect of diode current oil HPM. generation in the vircator system is discussed. The RPM pulse width has a strong connection with the diode current waveform. For most shots, corresponding to the Mine that microwave emissions starts, there is an inflection point in the diode current pulse. Compared with the Case that no microwave is generated, the diode current increases more slowly, following the inflection point. RPM generation terminates when Me beam current reaches the self-pinching critical Current of the diode.