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 F_max 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 Δλ_s at the position of maximum field F_max in the CS, and the end-on recorded wings broadening characteristic features shift Δλ_e. Individual Ne I and Ar I lines' correlation coefficients Δλ_s/Δλ_e are reported also. These coefficients can be used to estimate the maximum CS electric field F_max and the CS thickness d_c within reasonable margins of uncertainty in a standard analytical Grimm-type GD source with an end-on view available only.