Continuum drift kinetics applied to parallel heat transport*

The Chapman-Enskog like electron drift kinetic equation¹ provides kinetic closure of fluid equations and extends to the long mean free path regime of magnetized plasmas. In this work we discuss the application of a continuum numerical solution to this equation to provide closure for parallel heat flux in NIMROD. Accuracy is improved by expressing the equation in velocity coordinates using pitch-angle and speed normalized by the thermal speed. This leads to a tight coupling of temperature, T, to kinetic distortion, F, and demands a careful semi-implicit time advance for large time steps. Results are obtained from two integration schemes applied to a simultaneous advance of T and F: 1) Picard iteration, and 2) Newton's method. We compare the computational efficiency of both approaches. Additional parallelism was recently developed parallelizing the preconditioning step in the linear solver over speed collocation points in the velocity domain. We present the parallel scaling performance of this development. Using NIMROD we explore the effects of particle trapping on thermal transport in toroidal geometry in the presence of magnetic islands.

¹J. J. Ramos, Phys Plasmas 17, 082502 (2010).