Multiscale-optimized plasma turbulence simulation on petascale architectures

Abstract

We describe the mathematical formulation, outline the numerical discretization, and present performance analysis results for the CGYRO plasma turbulence code. The performance data was collected on 5 current leadership systems (2 KNL-based, 2 hybrid CPU-GPU and 1 Skylake-based). CGYRO is a relatively new gyrokinetic turbulence code, based on the well-known GYRO code, but redesigned from the ground up to operate efficiently on multicore and GPU-accelerated systems. The gyrokinetic equations specify a 5-dimensional distribution function for each species, with species coupled through both the Maxwell equations and collision operator. For the cross-machine performance analysis, we report and compare timings for 8 separate computational kernels. This kernel-based breakdown illustrates the strengths and weaknesses of the floating-point and communication architectures of the respective systems. We conclude with a preview of new multiscale turbulence results that are shown to accurately recover experimentally-observed electron turbulence levels in an ITER-baseline plasma regime that cannot be described using traditional long-wavelength simulation.