Modeling of Ionization and Recombination Processes in Plasma with Arbitrary Non-Maxwellian Electron Distributions

TL;DR

This paper develops methods to accurately compute ionization and recombination rates in plasma with non-Maxwellian electron distributions, crucial for astrophysical plasma diagnostics, and demonstrates their application to solar wind and magnetic reconnection scenarios.

Contribution

Introduces two fitting methods for non-Maxwellian electron distributions, enabling precise ionization and recombination rate calculations for astrophysical plasma analysis.

Findings

Ionization rates increase during electron acceleration, affecting temperature estimates.

Recombination rates decrease with high-energy tail distributions, impacting plasma diagnostics.

Methods show comparable accuracy to existing packages for kappa distributions.

Abstract

In astronomical environments, the high-temperature emission of plasma mainly depends on ion charge states, which requires accurate analysis of the ionization and recombination processes. For various phenomena involving energetic particles, the non-Maxwellian distributions of electrons exhibiting high-energy tails can significantly enhance the ionization process. Therefore, accurately computing ionization and recombination rates with non-Maxwellian electron distributions is essential for emission diagnostic analysis. In this work, we report two methods for fitting various non-Maxwellian distributions by using the Maxwellian decomposition strategy. For standard \{kappa} distributions, the calculated ionization and recombination rate coefficients show comparable accuracy to other public packages. We apply the above methods to two specific non-Maxwellian distribution scenarios: (I) accelerated electron distributions due to magnetic reconnection revealed in a combined MHD-particle simulation; (II) the high-energy truncated \{kappa} distribution predicted by the exospheric model of the solar wind. During the electron acceleration process, ionization rates of high-temperature iron ions increase significantly compared to their initial Maxwellian distribution, while the recombination rates may decrease due to the electron distribution changes in low-energy ranges. This can potentially lead to an overestimation of the plasma temperature when analyzing the Fe emission lines under the Maxwellian distribution assumption. For the truncated \{kappa} distribution in the solar wind, the ionization rates are lower than those for the standard \{kappa} distribution, while the recombination rates remain similar. This leads to an overestimation of plasma temperature when assuming a \{kappa} distribution.