Monte-Carlo approach to calculate the ionization of warm dense matter within particle-in-cell simulations

TL;DR

This paper introduces a Monte-Carlo based physical model integrated into particle-in-cell simulations to accurately compute ionization dynamics in warm dense matter, accounting for impact ionization, recombination, and plasma effects.

Contribution

The model is novel in self-consistently simulating ionization relaxation and can be applied to various compositions, improving accuracy over existing models near thermal equilibrium.

Findings

Including IPD increases ionization degree in aluminium WDM.

Neglecting recombination significantly overestimates ionization.

Model shows good agreement with Saha-Boltzmann and FLYCHK results.

Abstract

A physical model based on a Monte-Carlo approach is proposed to calculate the ionization dynam- ics of warm dense matters (WDM) within particle-in-cell simulations, and where the impact (col- lision) ionization (CI), electron-ion recombination (RE) and ionization potential depression (IPD) by surrounding plasmas are taken into consideration self-consistently. When compared with other models, which are applied in the literature for plasmas near thermal equilibrium, the temporal re- laxation of ionization dynamics can also be simulated by the proposed model. Besides, this model is general and can be applied for both single elements and alloys with quite different composi- tions. The proposed model is implemented into a particle-in-cell (PIC) code, with (final) ionization equilibriums sustained by competitions between CI and its inverse process (i.e., RE). Comparisons between the full model and model without IPD or RE are performed. Our results indicate that for bulk aluminium in the WDM regime, i) the averaged ionization degree increases by including IPD; while ii) the averaged ionization degree is significantly over estimated when the RE is neglected. A direct comparison from the PIC code is made with the existing models for the dependence of averaged ionization degree on thermal equilibrium temperatures, and shows good agreements with that generated from Saha-Boltzmann model or/and FLYCHK code.