VUV diagnostic of electron impact processes in low temperature molecular hydrogen plasma

TL;DR

This paper introduces novel VUV optical emission spectroscopy methods for diagnosing electron impact processes in low temperature molecular hydrogen plasma, improving accuracy by comparing rate coefficients of specific transitions.

Contribution

The paper presents new diagnostic techniques based on VUV emission spectroscopy that enhance understanding of plasma processes in molecular hydrogen, accounting for non-equilibrium electron and vibrational distributions.

Findings

Estimated rates of ionization and dissociation processes.

Reduced uncertainty in plasma process measurements.

Applied methods to filament arc discharge plasma.

Abstract

Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman-band ($B^1\Sigma^+_u \rightarrow X^1\Sigma^+_g$) and molecular continuum ($a^3\Sigma^+_g \rightarrow b^3\Sigma^+_u$), of the hydrogen molecule in VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-forbidden excitations reduces the uncertainty caused by the non-equilibrium distributions of electron energy and molecular vibrational level, which are typically known poorly in plasma sources. The described methods are applied to estimate the rates of various plasma processes in a filament arc discharge.