g4chargeit: Geant4-based kinetic Monte Carlo simulations of charging in dielectric materials

TL;DR

g4chargeit is a novel Geant4-based kinetic Monte Carlo framework that simulates time-dependent electrostatic charging in dielectric materials, capturing microscopic particle interactions and macroscopic charge phenomena.

Contribution

It introduces a self-consistent, multiscale simulation method for dielectric charging, integrating stochastic particle transport with electric field evolution, applicable to planetary regolith and beyond.

Findings

Charge accumulates in intergrain micro-cavities.

Electrostatic forces are consistent with experimental data.

Framework links microscopic events to macroscopic charge patches.

Abstract

We present g4chargeit, a kinetic Monte Carlo framework built on Geant4 for self-consistent simulation of time-dependent electrostatic charging in dielectric materials. The model explicitly incorporates stochastic particle transport and scattering processes using validated Geant4 cross-sections, while self-consistently evolving the electric potential and field. As a representative application, we simulate the charging of regolith grains under average dayside conditions on the Moon. The surface of the Moon, in addition to other airless planetary bodies, are regularly exposed to solar ultraviolet photons and solar-wind plasma, creating a radiation environment in which electrostatic interactions among regolith grains become significant. Until now, simulations of regolith charging have often relied on analytical approximations that oversimplify grain geometry and interaction mechanisms. Our Geant4-based simulations reveal charge accumulation within intergrain micro-cavities, leading to repulsive electrostatic forces consistent with experimental observations. The framework establishes a multiscale approach that links microscopic scattering events to the continuity equation of surface charge density and to the formation of macroscopic surface charge patches in complex grain geometries. Although demonstrated here for planetary regolith, the method is general and applicable to a broad range of dielectric charging problems. The code is openly available at https://github.com/kgandhi63/g4chargeit.git.