A graphics-card implementation of Monte-Carlo simulations for cosmic-ray transport

• A graphics-card implementation of a Monte-Carlo simulation is presented.
• Major applications are the diffusion of cosmic rays and solar energetic particles.
• Due to the SIMD model and shared memory, the code runs faster than the CPU version.
• The code decreases the computational cost of such simulations.
• The comparison with an existing implementation shows good agreement.

A graphics card implementation of a test-particle simulation code is presented that is based on the CUDA extension of the C/C++ programming language. The original CPU version has been developed for the calculation of cosmic-ray diffusion coefficients in artificial Kolmogorov-type turbulence. In the new implementation, the magnetic turbulence generation, which is the most time-consuming part, is separated from the particle transport and is performed on a graphics card. In this article, the modification of the basic approach of integrating test particle trajectories to employ the SIMD (single instruction, multiple data) model is presented and verified. The efficiency of the new code is tested and several language-specific accelerating factors are discussed. For the example of isotropic magnetostatic turbulence, sample results are shown and a comparison to the results of the CPU implementation is performed.