Classical molecular dynamic simulation to assess the non-Maxwellian behavior of inverse bremsstrahlung heating in weakly coupled plasmas

Abstract

Classical molecular-dynamics simulations (CMDS) have been conducted to investigate the non-Maxwellian behavior of a weakly coupled plasma submitted to the inverse bremsstrahlung heating of laser irradiation. It is the so called Langdon effect. It has important consequences on plasma properties. It reduces laser absorption, it modifies atomic physics due to its influence on the free electron population, it alters conduction and any other quantities that depends upon electron velocity distribution (EVD). Here, the Langdon effect has been studied with CMDS using the code LAMMPS where, contrary to Fokker-Plank simulations, widely used in the past, plasma many-body behavior at the microscopic level is taken into account self-consistently. For the first time with CMDS, we have observed the deformation of the instantaneous EVD in Langdon's condition. Anisotropy of these non-Maxwellian effects have been demonstrated at moderate and high intensities. CMDS results (related to the shape of the EVD and to the laser absorption reduction) do not match with previous Fokker-Planck simulations results as well as might have been expected. This should probably stimulate new developments to understand the complex many-body interaction of electrons and ions in a laser irradiated plasma in the future.