Leaked electrons from virtual cathode oscillation

We investigate the properties of leaked electrons from virtual cathode osci llation. It is found from a simulation that most leakage occurs from the ra dial edge of the beam, so that the leaked beam forms an annular beam. Axial bunching was also observed. The average leaked current was close to the sp ace-charge limiting current, and the energies of the electrons at the end o f the drift tube were a fraction of the injected energies, and were nearly independent of the injection currents. A preliminary experimental result se ems to support these simulation results.