Comparison of dust charging between Orbital-Motion-Limited theory and Particle-In-Cell simulations

TL;DR

This study compares the dust charge predictions of the modified Orbital-Motion-Limited theory with Particle-In-Cell simulations, demonstrating improved accuracy over previous approximations for large dust grains in plasma.

Contribution

The paper validates the revised OML theory against PIC simulations, establishing its applicability and accuracy for large dust grains in collisionless plasmas.

Findings

Revised OML predicts dust charge within 20% accuracy for r_d/λ_D ≤ 10.

Revised OML outperforms the Whipple approximation.

Collected currents and energy fluxes are accurate within 15-30%.

Abstract

The Orbital-Motion-Limited (OML) theory has been modified to predict the dust charge and the results were contrasted with the Whipple approximation [Tang and Delzanno, Phys. Plasmas 21, 123708 (2014)]. To further establish its regime of applicability, in this paper the OML predictions (for a non-electron-emitting, spherical dust grain at rest in a collisionless, unmagnetized plasma) are compared with Particle-In-Cell simulations that retain the absorption radius effect. It is found that for large dust grain radius $r_d$ relative to the plasma Debye length $\lambda_D$, the revised OML theory remains a very good approximation as, for the parameters considered ($r_d/\lambda_D\le10$, equal electron and ion temperatures), it yields the dust charge to within $20\%$ accuracy. This is a substantial improvement over the Whipple approximation. The dust collected currents and energy fluxes, which remain the same in the revised and standard OML theories, are accurate to within $15-30\%$.