Experimental verification of Boltzmann equilibrium for negative ions in weakly collisional electronegative plasmas

TL;DR

This study experimentally verifies that negative ions in weakly collisional electronegative plasmas are in Boltzmann equilibrium, providing insights into plasma structure and ion behavior in such environments.

Contribution

The paper presents the first experimental confirmation of Boltzmann equilibrium for negative ions in weakly collisional electronegative plasmas.

Findings

Negative ions are in Boltzmann equilibrium with a temperature of 0.06 eV.

The density ratio of negative ions to electrons ({eta}) is approximately 0.43.

No double layers separate the electronegative core and electropositive halo.

Abstract

Weakly collisional Ar-O2 electronegative plasmas are investigated in a dc multidipole chamber. An electronegative core and an electropositive halo are observed. The density ratio of negative ions to electrons ({\alpha}) in the nondrifting bulk is found to be 0.43. The profile of {\alpha} is found using both the phase velocity of ion acoustic waves and the drift velocity of positive ions determined by laser induced fluorescence. The experiment shows that negative ions are in Boltzmann equilibrium with a temperature of 0.06 \pm 0.02 eV. Double layers are not found separating the electronegative core and the electropositive halo.