Space-charge induced particle reflection between hybrid AC/DC biased electrodes

Abstract

Abstract Space-charge limited current flow between DC biased electrodes is a widely applicable problem in many areas of physics. Recently, radio-frequency biasing, together with DC self-bias formation, has been studied as a new concept for the extraction of charged particles from an upstream plasma source. Here, we compare particle extraction between systems using this hybrid AC/DC biasing, with conventional DC biased electrodes, and identify important similarity parameters. The injection current first leading to particle reflection strongly depends on the applied AC frequency and voltage magnitude, as well as the initial particle injection velocity, and is in general lower than the DC case. For injection currents above the AC limit, the system becomes unstable, and self-excited space-charge oscillations are generated. A critical parameter is the ratio of the average particle transit time between the electrodes to the AC period, γ = t L/T. As long as γ ≫ 1, the onset of particle reflection can be sufficiently delayed that the extracted current approaches the DC limit.