A FULLY IMPLICIT, TIME-DEPENDENT 2-D FLUID CODE FOR MODELING TOKAMAK EDGE PLASMAS

A fully implicit, time dependent 2-D fluid code is described that models the edge plasma region of a tokamak with a divertor or limiter. Equations solved are for particle continuity, parallel momentum, electron energy, ion energy, electrostatic potential, and neutral gas diffusion. We include the effects of parallel currents and cross-field drifts so that divertor biasing can be investigated. The core plasma is poloidally periodic, and the inner and outer private flux regions are properly connected. An implicit method-of-lines scheme is used to advance the variables in time utilizing the Krylov technique which does not require explicit formation or solution of the Jacobian matrix. However, for good performance, the problem needs to be preconditioned; a numerically generated Jacobian is used for this stage. The Jacobian can also be used to obtain the steady state solution by standard Newton iteration. Results are presented on the effects of biasing and parallel currents for DIII-D single-null parameters, and showing the time dependent heat flux on the divertor plate.