Initial microwave generation from the vircator system with various anode-cathode (A-K) gap distances

Summary form only given, as follows. The microwave output of vircator system has been shown to be dependent especially on diode anode-cathode (A-K) gap distance. The initial microwave generation time is delayed when the A-K gap distance has been increased from 2 to 8 mm in this experiment, and also it is shown that the central microwave frequency f is inversely scaled as the A-K gap distance. When the electron beam is generated from the cathode, the electrode sheath plasma is also generated just after the peak diode voltage on the electrodes, hence the perveance of diode is being varied to change the diode output characteristics at this moment. In our pulsed power system chundoong, the perveance characteristics had been experimentally investigated, from which the sheath plasma expansion speed could be found to be about 3 cm//spl mu/s inside the diode. It could be shown in this experiment that the microwave output power becomes to be maximum when the effective A-K gap distance due to the sheath plasma expansion becomes to be around 3 mm from the initial-set A-K gap distances. It means that there might be threshold effective A-K gap condition, at which the maximum microwave power could be achieved by virtual cathode oscillator formed by the injected electron beam current exceeding the space charge limited current.