Fokker-Planck calculations on heat flow in plasmas

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Abstract
This paper deals with the application of a Fokker–Planck code to the problem of heat conduction down steep thermal gradients. The results are compared with those obtained with other codes based on the Fokker–Planck equation in which various simplifying assumptions are made in the calculation of the Rosenbluth potentials. The particular problem considered is that of heat flow between spherical shells at different temperatures. The difference between the heat flows resulting from isotropic and anisotropic distributions is specially emphasized. The results show that, for calculating temperature, the usual Legendre polynomial expansion for the angular dependence of the distribution function gives reasonable results even when it is limited to two terms. However, the heat fluxes can differ by a factor of two when the Rosenbluth potentials are calculated from angular averages of the distribution function even when in the rest of the calculation the Legendre expansion is retained to all orders.