Quantifying ionization in hot dense plasmas

TL;DR

This paper investigates the challenge of defining ionization in hot dense plasmas and compares two methods for quantifying it, highlighting the importance of including specific electronic transitions for accuracy.

Contribution

The study introduces a comparison of continuum electron counting and optical conductivity methods for ionization, emphasizing the role of Pauli forbidden transitions in plasma modeling.

Findings

Up to 10% difference between the two ionization definitions.

Including Pauli forbidden transitions aligns conductivity-based ionization with counting methods.

Highlights the importance of electronic transition considerations in plasma ionization measurements.

Abstract

Ionization is a problematic quantity in that it does not have a well-defined thermodynamic definition, yet it is a key parameter within plasma modelling. One still therefore aims to find a consistent and unambiguous definition for the ionization state. Within this context we present finite-temperature density functional theory calculations of the ionization state of carbon in CH plasmas using two potential definitions: one based on counting the number of continuum electrons, and another based on the optical conductivity. Differences of up to 10\% are observed between the two methods. However, including "Pauli forbidden" transitions in the conductivity reproduces the counting definition, suggesting such transitions are important to evaluate the ionization state.