Disalignment rate coefficient of argon $\mathrm{2p_8}$ due to nitrogen collision

TL;DR

This paper presents a method using TDLIF measurements and a rate balance model to determine the disalignment rate constant of argon $ ext{2p}_8$ state caused by nitrogen collisions in a magnetized plasma, with results aligning well with molecular theory.

Contribution

It introduces a novel measurement and modeling approach to quantify nitrogen-induced disalignment rates of argon excited states in magnetized plasma conditions.

Findings

Disalignment rate constant for $ ext{2p}_8$ due to nitrogen was estimated.

Model predictions agree satisfactorily with molecular theory.

Method enables detailed analysis of optical emission in magnetized argon-nitrogen plasmas.

Abstract

Tunable diode laser induced fluorescence (TDLIF) measurements are discussed and quantitatively evaluated for nitrogen admixtures in argon plasma under the influence of a strong magnetic field. TDLIF measurements were used to evaluate light-transport properties in a strongly magnetized optically thick argon/nitrogen plasma under different pressure conditions. Therefore, a coupled system of rate balance equations was constructed to describe laser pumping of individual magnetic sub-levels of $\mathrm{2p_8}$ state through frequency-separated sub-transitions originating from $\mathrm{1s_4}$ magnetic sub-levels. The density distribution (alignment) of $\mathrm{2p_8}$ multiplet was described by balancing laser pumping with losses including radiative decay, transfer of excitation between the neighboring sub-levels in the $\mathrm{2p_8}$ multiplet driven by neutral collisions (argon and nitrogen) and quenching due to electron and neutral collisions. Resulting $\mathrm{2p_8}$ magnetic sub-level densities were then used to model polarization dependent fluorescence, considering self-absorption, which could be directly compared with polarization-resolved TDLIF measurements. This enables to estimate the disalignment rate constant for the $\mathrm{2p_8}$ state due to collisions by molecular nitrogen. A comparison to molecular theory description is given providing satisfactory agreement. The presented measurement method and model can help to describe optical emission of argon and argon-nitrogen admixtures in magnetized conditions and provides a basis for further description of optical emission spectra in magnetized plasmas.