Particle-in-cell code modelling of distribution functions and heat-flow

Heat-flow is of fundamental interest in plasmas with extreme temperature gradients. These plasmas can range from those found in laser-plasma experiments, to relativistic jets or tokamak divertors. Transport effects such as heat-flow are fundamentally driven by anisotropy within the distribution function. As anisotropy increases, the system is driven from local thermodynamic equilibrium (LTE). Fluid models, which often assume the anisotropy leads to only a small perturbation away from a Maxwellian distribution, can then fail to describe transport effects far from LTE accurately.

 

Here we describe how the kinetic modelling of plasmas using particle-in-cell (PIC) codes can aid in our understanding of plasmas as they are driven away from LTE. While often used to model collisionless phenomena, the inclusion of binary collision operators in PIC codes allows the investigation of collisional transport processes. As PIC codes do not assume the form of the distribution function they are well-suited to problems with substantial anisotropy. The regimes studied here are commonly encountered in high-energy-density systems, such as inertial confinement fusion experiments, where the mean-free-path of heat-carrying electrons and ions can exceed the plasma length scale causing the heat-flow to become non-local. These effects are modified by material interfaces and magnetic fields, which can then be explored using this platform.