Molecular dynamic simulations of electron heat conduction in weakly coupled plasmas

Classical molecular-dynamics simulations (CMDS) have been carried out on two components (electrons and ions) weakly coupled plasmas to investigate electron heat conduction (for Z=1) in situations where electron temperature gradient length is shorter or longer than electron-ion mean free path (respectively the free streaming limit and the diffusion limit).

In radiation-hydrodynamics codes, used to design ICF or HED experiments, it is customary to transit from a diffusive Spitzer-Harm (SH) [1] model (with an electron heat flux proportional to the electron-temperature gradient Q_SH = κ∇T_e ) to a free-streaming (FS) [2] model (with electron heat flux proportional to electron-temperature Q_FS = n_e v_th k_B T_e n) with help from a limitation Q = min(Q_SH , f Q_FS) where f is ranging from 0.03 to 0.15.

CMDS have allowed us to test both configurations (diffusive and FS) by setting a non-uniform spatial electron temperature profile and observing how it relaxes to a uniform profile as time goes by. In both situations, CMDS seem to shown that the evolution of the temperature profile evolves as a diffusion mechanism. CMDS suggest a limitation of the diffusion coefficient κ of the SH model in the free-streaming case rather than a drastic modification of the differential structure of the heat flux as suggested in [2].

[1] L. Spitzer and R. Harm, Phys. Rev., 89, 977 (1953)

[2] R. C. Malone et. al., Phys. Rev. Lett., 34, 721 (1975)