On determining the fraction of metastable ions produced by direct ionization

TL;DR

This paper develops a theoretical model and numerical simulations to accurately determine the fraction of metastable ions produced by direct ionization in plasma LIF measurements, addressing instrumental errors.

Contribution

It introduces a new theoretical model and numerical approach to correct for metastable lifetime effects in LIF measurements of plasma ions.

Findings

The model quantifies the impact of metastable lifetime on measurements.

Simulations demonstrate the correction method's effectiveness.

The approach improves the reliability of plasma diagnostics using LIF.

Abstract

Laser-induced fluorescence (LIF) is a powerful tool in studying wave-particle interactions, velocity-space diffusion and other phenomena in plasmas under the proper conditions. Ignoring the possible instrumental errors in LIF, such as metastable lifetime effects, may result in unreliable measurements. LIF is frequently performed on metastable states that are produced from direct ionization of neutral gas particles and ions in other electronic states. However, the metastable population born from neutrals cannot faithfully represent processes which act on the ion dynamics in a time shorter than the metastable lifetime. A numerical simulation is performed to study the metastable lifetime effects using a Lagrangian approach for LIF. A theoretical model in determining the fraction of metastable ions produced from direct ionization is reported to provide corrections to the LIF measurements.