Kinetics-only Delta-f (KODF): A PIC Method for Modeling RF Waves in Warm Plasma

We present a new delta-f particle-in-cell method, kinetics-only delta-f (KODF), and discuss its implementation in the Vorpal FDTD-PIC code [C. Nieter and J. R. Cary, J. Comp. Phys. 196, 448 (2004)]. 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 the deviation of the distribution function from equilibrium. KODF generalizes this concept to incorporate cold linear plasma waves into the known (quasi)analytic plasma behavior. Perturbations modeled by KODF are thus nonlinear, finite-temperature perturbations riding atop (and responding to) cold linear waves propagating through specified equilibrium profiles.



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