Gyrokinetic Modeling of Electrostatic Ion-Scale Turbulence in Divertor Tokamaks

Continuum gyrokinetic simulations of electrostatic ion scale turbulence are presented for the case of a diverted tokamak geometry. The simulation model, implemented in the finite-volume code COGENT, solves the long-wavelength limit of the full-F gyrokinetic equation for ion species coupled to the quasi-neutrality equation for electrostatic potential variations, where a fluid model is used for an electron response. The model describes the ion-scale ion temperature gradient and resistive drift modes as well as neoclassical ion physics effects. Regimes of enhanced and suppressed turbulence are observed depending on the plasma profiles, and the roles of a self-consistent background electric field and an X-point geometry are explored. In order to facilitate simulations of highly-anisotropic microturbulence, a numerical algorithm utilizing a locally field-aligned multiblock coordinate system is employed in COGENT. In addition, the efficiency of numerical calculations is improved by making use of implicit time integration and the use of spatially-dependent velocity normalization that can facilitate simulations with large variations in a background plasma temperature.