Molecular dynamic simulations to assess the non-Maxwellian behavior of inverse-bremsstrahlung heating in weakly coupled plasmas

Classical molecular-dynamics simulations (CMDS) with LAMMPS have been conducted on two components weakly coupled plasmas to investigate non-Maxwellian inverse bremsstrahlung (IB) absorption for moderate ionizations. After a brief description of our simulations restricted to plasmas with maxwellian electron velocity distribution (EVD) at Z = 1, we will present the results of simulations dedicated to the study of non-Maxwellian IB absorption at Z = 10. Deformation of EVDs in Langdon’s conditions is observed for the first time in CMDS. Different EVDs are observed depending upon intensity and initial plasma state, including anisotropic and isotropic supergaussians (predicted by Langdon). The relation between the order of the supergaussian and the laser intensity obtained by CMDS is qualitatively similar but quantitatively different from the one inferred from Fokker-Planck simulations. We have been able to produce a similar relation for the anisotropic orders (parallel to the direction of polarization and perpendicular to it) and found that the parallel order could exceed 5 (limit predicted by Langdon) whereas the perpendicular order remains below that limit. We will finally introduce a heating rate model to tentatively take into account these non-maxwellian effects.