Ultrahigh resolution simulations of mode converted ion cyclotron waves and lower hybrid waves Original Research Article

Full wave studies of mode conversion (MC) processes in toroidal plasmas have required prohibitive amount of computer resources in the past because of the disparate spatial scales involved. The TORIC code [Brambilla, Nucl. Fusion 38 (1998) 1805] solves the linear sixth order reduced wave equation for the ion cyclotron range of frequencies (ICRF), in toroidal geometry using a Fourier representation for the poloidal dimension and finite elements in the flux dimension. The range of problems that TORIC can do has been extended through both new serial algorithms and parallelization of memory and processing. The implementation of out-of-core memory management, FFT convolutions, and improved memory management brought MC studies just into range of the serial version of the code running on a NERSC Cray SV1. Some simple tests and arguments show that more resolution than is possible on a single processor system is needed to fully resolve these scenarios. By distributing the large linear system across many processors in conjunction with the out-of-core technique, the resolution limitations are effectively removed. ScaLAPACK is used to do the linear algebra operations and message passing interface (MPI) is used to distribute the significant amount of post-processing. The new parallel version of the code can easily do the most difficult MC problems on present day tokamaks (Alcator C-Mod and Asdex-Upgrade), with only 32 pc from a local Beowulf cluster. Using 48 or more processors admits us to problems in the lower hybrid range of frequencies.