Plasma bombardments in the diode in Ka-band coaxial transit-time oscillator

Plasma is a non-ignorable factor in a high power generator. In this paper, plasma bombardments in the diode region are found in experiment on a Ka-band transit-time oscillator. Microcosmic and energy dispersive analysis has been done first on the plasma spots. Based on the Carbon contents in different areas of the diode, a physical model describing the progress of the plasma from appearance to expansion is built. Subsequently, simulations on the plasma expansion have been done with particle-in-cell code calculation. The result agrees well with the model proposed above. Finally, a special structure is adopted in the improved Ka-band coaxial TTO to suppress or even avoid the plasma Bombardment. The study is of significance to generators for long-pulsed and repetition operation.