Specific Features of the Distribution of Atomic-Level Occupancies in Highly Ionized Helium Arc Plasma

Abstract

The near-threshold spectral region of radiation of helium arc plasma under atmospheric pressure and at an electron temperature of 3 eV was investigated. Under these conditions, plasma is ionizationally nonequilibrial due to the overwhelming predominance of recombination on a wall over the bulk recombination. It is shown that the occupancies of atomic levels n ≥ 4 rapidly decrease; therefore, no spectral lines from levels n ≥ 7 are observed. This fact is related to the destruction of excited atomic states in the quasi-static (ion) plasma microfield (mainly, in the nearest-ion field).