GPU-Accelerated Modeling of RF Propagation in a Full Tokamak Plasma

We have successfully ported the time-domain plasma model [1] in the VSim software [2,3] to run on large scale parallel GPU clusters. We present characteristics and benchmarks of the new algorithm’s operations. We demonstrate use of the algorithm on the ITER ICRF antenna and wall geometry, including diverter, with 2^nd order (cut-cell) accurate CAD defined geometries. The time-domain algorithm is locally implicit, spatially explicit, so that it can step over electron time scales without the need for global matrix inversion, e.g., it is ideally suited for GPU application. An important algorithmic improvement has also been made, and is demonstrated, which uses a sub-grid octant-averaging technique to eliminate noise on the order of 2Δx that was inherent in the original algorithm. This eliminates the need for costly filtering operations, and stencil enlargement, which further slowed down the CPU-based calculation. Continuing upgrades to the GPU based algorithm is also reported, with addition of self-consistent RF sheath physics being a priority.

[1] David N. Smithe, Finite-difference time-domain simulation of fusion plasmas at radiofrequency time scales, Physics of Plasmas 14, 056104 (2007)

[2] C. Nieter and J. Cary. 2004. VORPAL: a versatile plasma simulation code. J. Comput. Phys. 196, 2, 448-473.

[3] www.txcorp.com