Thermal Conductivity of a Laser Plasma*

We present a model supported by Vlasov—Fokker—Planck simulations of the electron thermal conductivity of a laser-produced plasma, which exhibits a reduced thermal conductivity at high laser intensity. A high-intensity laser reduces conductivity by forcing electrons away from equilibrium, resulting in depletion of both low-velocity bulk electrons and high-velocity tail electrons. Such an effect has been previously theorized, but never in a quantitative and practically useful form. We show that the tail electrons approximately follow a super-Gaussian distribution, but the exponent is distinct from that of the bulk. It is shown that in addition to the known dependence on ion charge, the thermal conductivity has a strong dependence on intensity through the parameter α=Zv_E²/v_T². For a value of α=0.5, the thermal conductivity is half its zero-intensity value. We distill our results into a simple analytic fit that can be readily implemented in any radiation-hydrodynamics code.