Time Integrator Agnostic Charge Conserving Finite Element PIC

TL;DR

This paper introduces a charge conserving particle-in-cell method compatible with any time integrator, eliminating the need for divergence cleaning and enabling stable, accurate plasma simulations with finite element methods.

Contribution

It develops a time integrator agnostic, charge conserving PIC methodology that satisfies Gauss' laws at every step, applicable to various finite element formulations.

Findings

Method works with wave equation FEM and Maxwell Solver FEM.

Successfully simulates single particle, beam, and plasma expansion scenarios.

Demonstrates stability and accuracy in complex plasma simulations.

Abstract

Developing particle-in-cell (PIC) methods using finite element basis sets, and without auxiliary divergence cleaning methods, was a long standing problem until recently. It was shown that if consistent spatial basis functions are used, one can indeed create a methodology that was charge conserving, albeit using a leap-frog time stepping method. While this is a significant advance, leap frog schemes are only conditionally stable and time step sizes are closely tied to the underlying mesh. Ideally, to take full advantage of advances in finite element methods (FEMs), one needs a charge conserving PIC methodology that is agnostic to the time stepping method. This is the principal contribution of this paper. In what follows, we shall develop this methodology, prove that both charge and Gauss' laws are discretely satisfied at every time step, provide the necessary details to implement this methodology for both the wave equation FEM and Maxwell Solver FEM, and finally demonstrate its efficacy on a suite of test problems. The method will be demonstrated by single particle evolution, non-neutral beams with space-charge, and adiabatic expansion of a neutral plasma, where the debye length has been resolved, and real mass ratios are used.