Plasma density effects on the electron impact ionization

TL;DR

This paper investigates how plasma density influences electron impact ionization by modeling ionization potential depression through plasma fluctuations and ion dynamics, leading to improved agreement with experimental data.

Contribution

It introduces a novel approach using a distribution of ionization energies derived from molecular dynamics to account for plasma fluctuations, improving ionization modeling accuracy.

Findings

Good agreement with experimental ionization potential depression data.

New analytical expression for ionization cross section considering fluctuations.

Enhanced understanding of plasma density effects on ionization processes.

Abstract

We present new results on the ionization by electron impacts in a dense plasma. We are interested in the density effect known as the ionization potential depression and in its role in atomic structure. Rather than using the well-known Stewart-Pyatt or Ecker-Kr\"oll formulas for the ionization potential depression, we consider a distribution function of the ionization energy, which involves the plasma fluctuations due to ion dynamics. This distribution is calculated within classical molecular dynamics. The removal of the noise yields a new distribution which is composed of a small set of Gaussian peaks among which one peak is selected by considering the signal-to-noise ratio. This approach provides an ionization potential depression in good agreement with experimental results obtained at the Linac Coherent Light Source facility. Our results are also compared to other calculations. In a second part, we investigate the effects of the ionization potential depression and the fluctuations on ionization by electron impacts. We propose a new expression of the cross section, based on an average over the ionization energy distribution. This cross section can be calculated analytically. The main strength of our work is to account for the fluctuations due to ion dynamics.