ELECTRON-BEAM BEHAVIOR IN AN AXIALLY-EXTRACTED VIRTUAL CATHODE OSCILLATOR

High-power microwave generation in an axially-extracted virtual cathod e oscillator has been studied experimentally. The microwave emission o f 120 MW at frequencies in the range of 10-12 GHz is observed in the p resence of annular electron beam operated at a 300 kV and 20 kA. The e lectron beam current in the diode region is well characterized by the electron space charge-limited current in bipolar flow, which is well b elow the critical current defined for diode pinching. The observed mic rowave emission is accompanied by the strongly pinched electron beam. Essential feature of such a pinching effect for the microwave generati on is confirmed by the absence of emission when the pinch of electron beam is suppressed by the application of the axial magnetic field.