NONLOCAL ELECTRON-TRANSPORT IN LASER CREATED PLASMAS

The classical linear Spitzer-Harm formula has been shown to lead to an overestimation of the electron heat flux in laser-plasma interaction experiments. We briefly review the classical theory of heat transport in a plasma, and give a simplified demonstration of the Spitzer-Harm f ormula. The electron heat conductivity is calculated for a large value of the ion charge Z. Correction due to a finite value of Z is evaluat ed with a simplified electron-electron collision operator. We then sho w that in a steep temperature gradient, the collisional mean free path of the electrons that transport the energy may be larger than the sca le length of the temperature gradient. In this case the Spitzer-Harm f ormula overestimates the actual heat flux in the main part of the temp erature gradient, and predicts a too small heat fur slightly away from the location of the large temperature gradient. A nonlocal macroscopi c formula, which is a sort of convolution of the Spitzer-Harm heat flu x by a delocalization function, is shown to accurately describe the el ectron heat flow in both smooth and steep temperature gradients. This nonlocal formula for the heat flow is analytically justified. A select ion of slightly different delocalization functions proposed in the lit erature is compared to the original one and to the results of Fokker-P lanck calculations of the heat flow.