The Gaussian Radial Basis Function Method for Plasma Kinetic Theory

TL;DR

This paper introduces a novel Gaussian Radial Basis Function method for discretizing the plasma kinetic system, including the complex Fokker-Planck collision operator, enabling more accurate and efficient simulations of magnetized plasmas.

Contribution

The paper presents a new RBF-based discretization approach for the plasma kinetic equations, particularly handling the Fokker-Planck collision operator analytically.

Findings

Successfully derived 2D and 3D numerical solutions of the nonlinear Fokker-Planck equation.

Demonstrated the method's suitability for astrophysical and laboratory plasma applications.

Connected the RBF approach to plasma fluid theories.

Abstract

A fundamental macroscopic description of a magnetized plasma is the Vlasov equation supplemented by the nonlinear inverse-square force Fokker-Planck collision operator [Rosenbluth et al., Phys. Rev., 107, 1957]. The Vlasov part describes advection in a six-dimensional phase space whereas the collision operator involves friction and diffusion coefficients that are weighted velocity-space integrals of the particle distribution function. The Fokker-Planck collision operator is an integro-differential, bilinear operator, and numerical discretization of the operator is far from trivial. In this letter, we describe a new approach to discretize the entire kinetic system based on an expansion in Gaussian Radial Basis functions (RBFs). This approach is particularly well-suited to treat the collision operator because the friction and diffusion coefficients can be analytically calculated. Although the RBF method is known to be a powerful scheme for the interpolation of scattered multidimensional data, Gaussian RBFs also have a deep physical interpretation as local thermodynamic equilibria. In this letter we outline the general theory, highlight the connection to plasma fluid theories, and also give 2D and 3D numerical solutions of the nonlinear Fokker-Planck equation. A broad spectrum of applications for the new method is anticipated in both astrophysical and laboratory plasmas.