Particle and Heat Equilibration in the Presence of Magnetic Islands

Eric Held, University of Wisconsin, Madison

A fundamental problem for bootstrap current-driven magnetic islands is to understand the dynamics and profile properties of density and electron temperature. Although electron temperature flattening inside the island separatrix has been observed, it is uncertain the degree to which density profiles show a similar flattening. To study the evolution of density and electron temperature in a helical island geometry, we solve the coupled parallel momentum and continuity equations in the presence of a slower-growing magnetic perturbation that simulates the evolution of a neoclassical tearing mode. It is assumed that sound wave propagation along field lines is primarily responsible for equilibration, of density over perturbed flux surfaces. Electron temperature equilibration, on the other hand, occurs on perturbed flux surfaces as a result of a rapid parallel heat flux. Properly accounting for this heat flux requires a solution of an appropriate kinetic equation that takes into account free-streaming and collisional effects in a helical magnetic geometry. An analytic closure for the heat flux is constructed based on a multiple time and spatial scale scale, Chapman-Enskog-like analysis. This heat flux is then inserted into a temperature evolution equation which is solved in the presence of an evolving helical magnetic island.

Abstract Author(s): Eric Held