Ionization equilibrium of nitrogen under kappa electron distributions

School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China

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Received: 1 July 2025
Accepted: 23 February 2026

Abstract

Non-Maxwellian electron energy distributions, such as kappa distributions, have been proposed to explain discrepancies in observed astrophysical plasmas. We employed the coronal approximation to study the level populations of ionized nitrogen under kappa distributions across a range of electron temperatures and densities. Both ground and metastable levels were considered. We propose a novel density diagnostic method that combines these level populations with spectroscopic measurements: level-resolved cross sections for key atomic processes – electron impact ionization, photoionization (PI), radiative recombination, and dielectronic recombination (DR) – are calculated using the level-to-level distorted wave method in the Flexible Atomic Code, generalized for kappa distributions, and the corresponding rate coefficients are then derived. Using these coefficients, we computed the ionization equilibrium, with a particular focus on the roles of DR and PI. We also investigated the suppression of DR by electron density and its influence on the resulting ionization equilibrium.