Argonne National Laboratory

Improved Nonlinear Solvers in BOUT++

TitleImproved Nonlinear Solvers in BOUT++
Publication TypeJournal Article
Year of Publication2012
AuthorsDudson, B, Farley, S, McInnes, LCurfman
Date Published08/2012
Other NumbersANL/MCS-P3025-0812

Challenging aspects of large-scale turbulent edge simulations in plasma physics include robust nonlinear solvers and efficient preconditioners. This paper presents recent advances in the scalable solution of non-linear partial di fferential equations in BOUT++, with emphasis on simulations of edge localized modes in tokamaks. A six-field, nonlinear, reduced magnetohydrodynamics model containing the fast shear Alfven wave and electron and ion heat conduction along magnetic fi elds is solved by using Jacobian-free Newton-Krylov (JFNK) methods and nonlinear GMRES (NGMRES). Physics-based preconditioning based on analytic Schur factorization of a simplifi ed Jacobian is found to result in an order of magnitude reduction in runtime over unpreconditioned JFNK, and NGMRES is shown to signifi cantly reduce runtime while requiring only the nonlinear function evaluation. We describe in detail the preconditioning algorithm, and we discuss parallel performance of NGMRES and Newton-Krylov methods using the PETSc library.