Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

摘要

The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, chi(r), due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w(2)(chi(parallel to)chi(perpendicular to))(1/2) for sufficiently high values of chi(parallel to)/chi(perpendicular to), where chi(parallel to)/chi(perpendicular to) is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of chi(parallel to)/chi(perpendicular to), however, the maximum value of chi(r) is proportional to w(4)chi(parallel to). In a locally stochastic magnetic field, chi(r) is again proportional to w(4)chi(parallel to) for low chi(parallel to)/chi(perpendicular to), which is in agreement with the analytical results. With increasing chi(parallel to)/chi(perpendicular to), chi(r) is dominated first by the additive effect of individual islands and then by the field ergodicity.