Electric field development in γ-mode radiofrequency atmospheric pressure glow discharge in helium

Abstract

Time development of electric field strength during radio-frequency sheath formation was measured using Stark polarization spectroscopy in a helium γ-mode radio-frequency (RF, 13.56 MHz) atmospheric pressure glow discharge at high current density (3 A cm−2). A method of time-correlated single photon counting was applied to record the temporal development of spectral profile of He I 492.2 nm line with a sub-nanosecond temporal resolution. By fitting the measured profile of the line with a combination of pseudo-Voigt profiles for forbidden (2 1P–4 1F) and allowed (2 1P–4 1D) helium lines, instantaneous electric fields up to 32 kV cm−1 were measured in the RF sheath. The measured electric field is in agreement with the spatially averaged value of 40 kV cm−1 estimated from homogeneous charge density RF sheath model. The observed rectangular waveform of the electric field time development is attributed to increased sheath conductivity by the strong electron avalanches occurring in the γ-mode sheath at high current densities.