Modeling of bound electron effects in particle-in-cell simulation

TL;DR

This paper introduces a new model for particle-in-cell simulations that accounts for bound electron effects by representing ions as structured particles with a nucleus and electron cloud, enabling more accurate modeling of laser interactions with partially ionized media.

Contribution

The paper presents a novel PIC model incorporating bound electron effects through structured ions, improving the simulation of laser interactions with partially ionized materials.

Findings

Successfully modeled laser scattering in partially ionized media.

Simulated laser propagation and Bragg scattering in crystal structures.

Potential applications in x-ray laser-driven phenomena and nonlinear optical materials.

Abstract

To include the bound electron effects in particle-in-cell (PIC) simulation, we propose a model in which the response of the dipole components of partially ionized ions to external electromagnetic fields can be included. Instead of treating the macro-ion particle as a single particle without an internal structure, the ions are considered to have a structure composed of a central nucleus and a bounded electron cloud in our model. The two parts experience the interactions of both the external electromagnetic fields and the internal Coulomb fields. In this way, the laser scattering effects by a partially ionized medium can be modeled properly in the PIC simulation. The laser propagation in a neutral medium and the Bragg scattering of the laser in crystal structure have been simulated with a PIC code modified based on our model as the benchmark. Our model may find applications to study some interesting problems, such as the x-ray laser-driven wakefield acceleration in crystals, the x-ray laser-driven high energy density physics, and intense laser propagation in partially ionized nonlinear optical materials, etc.