Particle-in-cell simulation in contact with a chaotic thermostat

This investigation explores the properties of a particle-in-cell (PIC) simulation in which the interacting particles are simultaneously in contact with a chaotic thermostat [G. J. Morales, Phys. Rev. E 99, 062218 (2019)]. The role of the thermostat is to maintain a Maxwellian velocity distribution function having a prescribed temperature through deterministic, chaotic orbits. In the absence of a self-consistent electric field, it has been previously established [G. J. Morales and Z. Li, Phys. Plasmas 30, 032104 (2023)] that the wave–particle interaction in this environment follows the generalized collisional plasma dispersion function [B. D. Fried et al., Phys. Fluids 9, 292 (1966)]. This implies that the particle response automatically evolves from the collisionless Landau limit to the Braginskii collisional behavior as the coupling time scale to the thermostat is varied. The present work documents the ensuing collective behavior for a variety of situations, including heating and cooling to Maxwellian distributions of prescribed temperatures, relaxation of an initial drift, response to a DC electric field, Debye shielding of spatially periodic sources, externally driven traveling waves, and relaxation of the two-stream instability. In addition to the usual collective Langmuir waves, it is found that the system supports modes associated with the thermostat dynamics. These modes become more prominent as the effective collision frequency becomes comparable to the plasma frequency.