Electric field measurement in gas discharges using stark shifts of He I lines and their forbidden counterparts

Abstract

A spectroscopic method for the measurement of macroscopic electric field strength in discharges, based on Stark shifts of several helium emission lines with their forbidden counterparts, is presented. The shifts of forbidden and allowed π components are calculated for eight line groups of helium. For practical use, polynomial functions are provided for the shifts of line groups applicable in the visible range. The method is an extension and improvement of a previously established method for two line groups. Line fitting procedures are presented that take into account components of a given helium line group, provide higher accuracy compared to simple evaluation, and enable measurements of lower field values. The method and fitting procedure were experimentally tested and verified by measuring the field distribution in the cathode fall of a low pressure glow discharge. Due to its ab initio basis the presented method can be used for measuring electric field distributions in various types of discharges, independently of other plasma parameters and fulfillment of special conditions.

Plasma-surface interaction: dielectric and metallic targets and their influence on the electric field profile in a kHz AC-driven He plasma jet

“…The method is based on the work of Foster [27] and well described in more recent publications [28][29][30]. The electric field strength value can be determined from the distance between the allowed and the forbidden Helium line and is given by the formula [31]:…”

Influence of a target on the electric field profile in a kHz atmospheric pressure plasma jet with the full calculation of the Stark shifts

“…In this paragraph, the resulting relation between Δλ AF and the electric field is compared to the relation obtained from Cvetanovic et al, 8 Foster, 20 and Kuraica. 24 The supplementary material of Cvetanovic et al gives the wavelength shift of the different n ¼ 4 levels for the He I 447.1 nm line and the He I 492.2 nm line, as a function of the electric field (ranging from 0 kV/cm to 101 kV/cm, in steps of 1 kV/cm).…”

“…The characteristics of the electric field, among which is the space and time evolution of the electric field, commonly determine the energy and flux of the charged particles in the plasma and thus determine the behavior of the discharge. 8 Therefore, it is essential to know the electric field inside the plasma jet, especially when it is interacting with a target. Measuring the electric field however is not trivial, since the plasma is influenced when, for example, a Langmuir probe is placed near or inside the plasma jet.…”

Electric field measurement in the dielectric tube of helium atmospheric pressure plasma jet

“…More details about electric field measurement using this method in low pressure glow discharge, DBD, plasma jet, and radiofrequency atmospheric pressure discharge in helium can be found in our previous publications. [17][18][19][32][33][34][35][36][37][38][39] The method is based on the measurements of the distance between two helium lines, forbidden and allowed, which are shifting depending on the value of the external electric field. In order to separate two polarized components of the emitted light, plastic polarizer was mounted in front of the slit, and only p-polarized light was recorded.…”