Study On Heat Transport Across Stochastic Magneticfield And Its Effect On The Instability Of The Tearing Mode

The study of the heat diffusion in Tokamak plasmas is an important part of anomalous heat transport. The heat diffusion across the single island and the stochastic magnetic field is studied numerically. The parameter /cw w, is found to be an important parameter in charactering the transport, where w is the magnetic island width, and cw is the critical island width for flattening the electron temperature across an island. For a single island, the enhanced radial heat diffusivity, ??, due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat diffusivity r? normalized to the perpendicular heat conductivity ?? at the rational surface is proportional to 4( /)cw w for w/ w 1c?. For w/ w 3c?, however, the maximum value of r? normalized to ?? is proportional to 2( /)cw w. There is a transition region between these two slopes around / 1.8cw w ?.The stochastic field is generated by the overlap of two magnetic islands. The parameter /cw w, is also an important parameter. For / 1cw w ?, the enhanced radial heat diffusivityr? is proportional to the parallel heat diffusivity ?, and the heat transport is dominated by the additive effect of individual islands. For / 3cw w ?,r? is also proportional to ? and the additional degradation of the energy confinement due to stochastic magnetic field becomes apparent. From / 1cw w ? to 3, there is a transition region, where r? increases slowly with ?.No matter whether it is a high magnetic shear or low magnetic shear, the enhanced radial heat diffusivityr? approximately has the same relationship with ?.