Specific features of the distribution of atomic-level occupancies in highly ionized helium arc plasma

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 $n \ge 4$ rapidly decrease; therefore, no spectral lines from levels $n \ge 7$ 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).