Overcoming timestep limitations in boosted-frame Particle-In-Cell simulations of plasma-based acceleration

TL;DR

This paper introduces a CFL-free spectral solver for boosted-frame Particle-In-Cell simulations, enabling larger timesteps and overcoming traditional limitations, which significantly enhances simulation efficiency in plasma-based acceleration modeling.

Contribution

The authors develop a spectral solver that removes CFL constraints in boosted-frame PIC simulations, allowing larger timesteps and improved computational speed.

Findings

Enables larger timesteps in boosted-frame PIC simulations.

Reduces numerical instabilities at large timesteps.

Achieves significant speed-up in plasma acceleration simulations.

Abstract

Explicit electromagnetic Particle-In-Cell (PIC) codes are typically limited by the Courant- Friedrichs-Lewy (CFL) condition, which implies that the timestep multiplied by the speed of light must be smaller than the smallest cell size. In the case of boosted-frame PIC simulations of plasma-based acceleration, this limitation can be a major hinderance as the cells are often very elongated along the longitudinal direction and the timestep is thus limited by the small, transverse cell size. This entails many small-timestep PIC iterations, and can limit the potential speed-up of the boosted-frame technique. Here, by using a CFL-free analytical spectral solver, and by mitigating additional numerical instabilities that arise at large timestep, we show that it is possible to overcome traditional limitations on the timestep and thereby realize the full potential of the boosted-frame technique over a much wider range of parameters.