Diagnostics of small plasma discharges using probing in wide range of microwave frequencies

Abstract

A diagnostic method for small and microcavity plasma discharges is proposed. The method is based on applying a weak variable-frequency probing signal to the same electrodes that are used to create the plasma and measuring the reflected signal's amplitude and phase over a wide frequency range. Thus, the discharge impedance at multiple probing frequencies may be found, and the key plasma discharge parameters, such as the electron density and temperature and the sheath thickness, can be inferred. The method is dubbed SPRIGHT (Small Plasma Reflection Inter-rogation with GigaHertz Transmitter) and is demonstrated for a small (2 mm interelectrode gap) radio frequency capacitively coupled discharge in argon at pressures of 1–5 Torr.