Massively Parallel Three-Dimensional Toroidal Gyrokinetic Flux-Tube Turbulence Simulation

A massively parallel three-dimensional nonlinear gyrokinetic flux-tube simulation model is discussed. This simulation is used to study turbulent heat transport in core tokamak fusion plasmas. This model allows for high resolution simulations of ion-temperature-gradient-driven turbulence using realistic plasma parameters assuming locality of the turbulent fluctuations. The simulation model, computational techniques, and parallel algorithms are discussed. The use of field-aligned coordinates allows for a natural domain decomposition in the direction along the magnetic field with good parallel performance. Digital filtering along the field line maintains proper toroidal and poloidal periodicity. A new approach to parallelization, “domain cloning,” is presented. Domain cloning is another layer of parallelization. It is an alternative to a two-dimensional domain decomposition and may be useful for clustered symmetric-multiprocessor machines. Performance results are presented for two high-performance massively parallel computers.