Minisymposium Presentation

We report progress on the development and application of a hybrid gyrokinetic ion–fluid electron model for simulations of cross-separatrix plasma transport in the edge region of a divertor tokamak. The hybrid model includes ion-scale ion temperature gradient (ITG) and resistive drift and ballooning modes, as well as neoclassical ion physics and orbit loss effects. The model is implemented in the finite-volume gyrokinetic code COGENT, which employs a locally field-aligned coordinate system combined with mapped multi-block grid technology to handle strongly anisotropic edge plasma turbulence. Additionally, COGENT utilizes a flexible implicit-explicit (IMEX) time integration framework that can handle the temporal multiscale nature of plasma transport. To that end, the 5D high-dimensional kinetic part of the system that involves ion parallel transients and diamagnetic drift time scales is treated explicitly. The 3D low-dimensional fluid part of the system that contains fast electron physics and Alfven-wave time scales is treated implicitly. The performance of the IMEX scheme is optimized by developing specialized preconditioners for the electrostatic and electromagnetic versions of the hybrid model. Verification results and simulations in realistic single-null geometries are presented.

*Work performed for USDOE, at LLNL under contract DE-AC52-07NA27344.