BOUT++: A framework for parallel plasma fluid simulations

A new modular code called BOUT++ is presented, which simulates 3D fluid equations in curvilinear coordinates. Although aimed at simulating Edge Localised Modes (ELMS) in tokamak x-point geometry, the code is able to simulate a wide range Of fluid models (magnetised and unmagnetised) involving an arbitrary number of scalar and vector fields, in a wide range of geometries. Time evolution is fully implicit, and 3rd-order WENO schemes are implemented. Benchmarks are presented for linear and nonlinear problems (the Orszag-Tang vortex) showing good agreement. Performance of the code is tested by scaling with problem size and processor number, showing efficient scaling to thousands of processors. Linear initial-value simulations of ELMS using reduced ideal MHD are presented, and the results compared to the ELITE linear MHD eigenvalue code. The resulting mode-structures and growth-rate are found to be in good agreement (gamma(BOUT++) = 0.245 omega(A), gamma(ELITE) = 0.239 omega(A), with Alfvenic timescale 1/omega(A) = R/V-A). To our knowledge, this is the first time dissipationless, initial-value Simulations of ELMS have been successfully demonstrated. (C) 2009 Elsevier B.V. All rights reserved.