Estimation of the maximum electric field strength in the cathode sheath of a Grimm-type glow discharge by end-on view optical emission spectroscopy in neon and argon

Abstract

We present a series of optical emission spectroscopy (OES) measurements of the stable correlation in characteristic features of spectral line shapes of neutral neon and argon, recorded in the Grimm-type plane cathode DC glow discharge (GD) source from two positions: (1) perpendicular to the cathode surface from the end of the discharge, in line with the discharge axis (end-on view) and (2) side-on cathode view, parallel to the cathode surface and perpendicular to the discharge axis, at the position of the maximum external electric field Fmax in the cathode sheath (CS), close to the cathode surface. Side-on view recording enables spatially resolved OES in the CS, where the Stark effect decisively determines the splitting and shifting of line components relative to the unshifted zero-field line. On the other hand, commonly available end-on view spectra recording in standard analytical Grimm-type sources collects integral light emission from the different layers of the discharge, both CS and negative glow (NG). However, distinct Stark components of several Ne I and Ar I lines' splitting and shifting in the CS are preserved as characteristic excessive wings broadening features in the end-on recordings as well. Following spectral measurements of six Ne I and four Ar I lines in a broad range of discharge conditions (pressure, voltage, current) and cathode materials, we report on a sustained correlation coefficient of 1.083 in neon and 1.129 in argon between the side-on recorded components shift Δλs at the position of maximum field Fmax in the CS, and the end-on recorded wings broadening characteristic features shift Δλe. Individual Ne I and Ar I lines' correlation coefficients Δλs/Δλe are reported also. These coefficients can be used to estimate the maximum CS electric field Fmax and the CS thickness dc within reasonable margins of uncertainty in a standard analytical Grimm-type GD source with an end-on view available only.