Numerical modeling of diffusive heat transport across magnetic islands and highly stochastic layers

摘要

Diffusive heat transport across magnetic islands and highly stochastic layers is studied numerically for realistic values of chi(parallel to)/chi(perpendicular to) in cylindrical geometry, where chi(parallel to) denotes the heat diffusion coefficient parallel and chi(perpendicular to) the one perpendicular to the magnetic field lines. The computations are performed with a second-order finite difference scheme, for which the numerical errors are independent from the value of chi(parallel to)/chi(perpendicular to) +AFs-S. Gunter et al., J. Comput. Phys. 209, 354 (2005)+AF0-. Sufficient spatial resolution is ensured by using an unsheared helical coordinate system. The heat flux around magnetic islands as well as the effective radial heat diffusivity chi(r) are examined and compared to analytical theory. The temperature perturbations caused by magnetic islands and the resulting bootstrap current perturbations essential for the stability of neoclassical tearing modes are analyzed and compared to analytical predictions +AFs-R. Fitzpatrick, Phys. Plasmas 2, 825 (1995)+AF0-. Agreement is found in the +ACI-small+ACI- and +ACI-large+ACI- island limits, but an enhanced NTM drive is observed in between. A correction factor that can reproduce the numerical results very well is presented. For a highly stochastic layer, produced by five strongly overlapping islands, the radial heat diffusivity chi(r) is determined and compared to several analytical theories. (C) 2007 American Institute of Physics.