Speeding Up Simulations By Slowing Down Particles: Speed-Limited Particle-In-Cell Simulation

TL;DR

SLPIC is a novel particle-in-cell method that accelerates plasma simulations by slowing down particles, enabling larger timesteps and significantly reducing computation time while maintaining accuracy.

Contribution

The paper introduces SLPIC, a speed-limited PIC technique that allows explicit large-timestep kinetic plasma simulations without sacrificing first-principles physics.

Findings

Achieved a 160x speed-up in plasma sheath simulation.

Maintained accuracy comparable to standard PIC methods.

Enabled feasible kinetic simulations in regimes previously requiring fluid models.

Abstract

Based on the particle-in-cell (PIC) plasma simulation method, the speed-limited PIC (SLPIC) method delivers faster kinetic plasma simulation in cases where the particle distributions evolve slowly compared with the maximum stable PIC timestep. SLPIC thus offers more feasible, fully kinetic simulation in regimes that historically have required fluid approaches, such as magnetohydrodynamic (MHD), two-fluid, or Boltzmann electron treatments. In particular, SLPIC allows an explicit time advance with steps much larger than the inverse plasma frequency, avoiding the instability explicit PIC faces with large timesteps. SLPIC avoids this instability by slowing down fast particles (e.g., electrons) in a way that is rigorously underpinned by an approximate Vlasov equation; unlike MHD, two-fluid, and Boltzmann electron approaches, SLPIC does not fundamentally neglect any first-principles plasma physics, although the choices of grid cell size, timestep, and number of macroparticles per cell naturally limit the physical phenomena that can be accurately represented. SLPIC can be implemented with minor modifications of a standard PIC code and does not require an implicit time advance. It enables large timesteps in first-principles kinetic plasma simulation of appropriately slow phenomena, and it can handle many of the same complications as PIC, such as boundary conditions and collisions. In an argon plasma sheath test problem, a SLPIC simulation achieved a speed-up of a factor of 160 over the corresponding PIC simulation, without loss of accuracy.