Modeling Ion Bernstein Waves with Kinetics-Only Delta-F PIC Methods

We present a new delta-f particle-in-cell method, kinetics-only delta-f (KODF), and discuss both its physics applications and its implementation in the Vorpal FDTD-PIC code. In conventional delta-f methods, computational markers (‘particles’) evolve along characteristic trajectories to model perturbations around a known equilibrium distribution function. The markers need not model the equilibrium distribution (as in total-f approaches); instead, marker weight variables track deviations of the distribution function from equilibrium. KODF generalizes this concept to include cold linear plasma waves in the known (quasi)analytic plasma behavior. Perturbations modeled by KODF are thus nonlinear, finite-temperature perturbations riding atop/responding to cold linear waves propagating through specified equilibrium profiles.



In our implementation, semi-implicit FDTD methods [Smithe, PoP 14 056104 (2007)] model the fluid behavior of cold plasma waves, and source terms arising from these waves (e.g. gradients of cold current/charge densities) drive and evolve responsive warm plasma effects in the KODF weight evolution equation. We explore noise-reduction capabilities of the KODF algorithm and its ability to model waves of interest in RF heating scenarios (e.g. mode-converted IBWs).