Effect of Nonlinear Energy Transport on Neoclassical Tearing Mode Stability in Tokamak Plasmas

摘要

An investigation is made into the effect of the reduction in anomalousperpendicular electron heat transport inside the separatrix of a magneticisland chain associated with a neoclassical tearing mode in a tokamak plasma,due to the flattening of the electron temperature profile in this region, onthe overall stability of the mode. The onset of the neoclassical tearing modeis governed by the ratio of the divergences of the parallel and perpendicularelectron heat fluxes in the vicinity of the island chain. By increasing thedegree of transport reduction, the onset of the mode, as the divergence ratiois gradually increased, can be made more and more abrupt. Eventually, when thedegree of transport reduction passes a certain critical value, the onset of theneoclassical tearing mode becomes discontinuous. In other words, when somecritical value of the divergence ratio is reached, there is a suddenbifurcation to a branch of neoclassical tearing mode solutions. Moreover, oncethis bifurcation has been triggered, the divergence ratio must reduced by asubstantial factor to trigger the inverse bifurcation.