BOUT

Application of parallel implicit methods to edge-plasma numerical simulations. A description is given of the parallelization algorithms and results for two codes used extensively to model edge plasmas in magnetic fusion energy devices. The codes are UEDGE, which calculates two-dimensional plasma and neutral gas profiles over long equilibrium time scales, and BOUT, which calculates three-dimensional plasma turbulence using experimental or UEDGE profiles. Both codes describe the plasma behavior using fluid equations. A domain decomposition model is used for parallelization by dividing the global spatial simulation region into a set of domains. This approach allows the use of a recently developed Newton-Krylov numerical solver, PVODE. Results show nearly an order of magnitude speedup in execution time for the plasma transport equations with UEDGE when the time-dependent system is integrated to steady state. A limitation that is identified for UEDGE is the inclusion of the (unmagnetized) fluid gas equations on a highly anisotropic mesh. The speedup of BOUT scales nearly linearly up to 64 processors and gets an additional speedup factor of 3--6 by using the fully implicit Newton-Krylov solver compared to an Adams predictor corrector. The turbulent transport coefficients obtained from BOUT guide the use of anomalous transport models within UEDGE, with the eventual goal of a self-consistent coupling.