GPU acceleration of DEMO particle exhaust simulations

Abstract

In this work we present an implementation of accelerating the calculation of neutral gas flow in a single-null DEMO divertor configuration on a graphics processing unit (GPU), using the DIVGAS (divertor gas simulator) code. For comparison purposes, various types of GPUs will be used, which include pure GPUs for scientific calculations as well as GPUs for gaming purposes. The computation accuracy of the DIVGAS code on GPUs has been validated with the corresponding CPU-based benchmark case. To evaluate the performance gains, the computing time on each GPU against its sequential CPU counterpart has been compared. The measured speedups show that the GPU can accelerate the execution of the DIVGAS code by a factor of 60. The speedup of the DIVGAS code scales linearly with the corresponding double precision peak performance of the GPU as well as the GPU memory bandwidth. The parallelization approach presented here significantly reduces the cost of DIVGAS simulations and has the potential to scale to large CPU/GPU clusters, which could enable future applications, which focus on even more complex 3D neutral flow problems. The accelerated version of the DIVGAS code on GPUs is considered to be a major breakthrough in the reduction of the needed computational time for fusion related applications.

Divertor enrichment of recycling impurity species (He, N2, Ne, Ar, Kr) in ASDEX Upgrade H-modes

“…Neutral impurities are entrained in the viscous D 2 flow, resulting in an increase of their effective conductances [4]. This effect will be discussed along calculations with the Monte Carlo code DIVGAS [15] described in section 2.1. The impurity entrainment in the D 2 flow can be experimentally tested using the particle removal time, which is dominated by the effective pumping speed.…”

“…The situation is less clear for seed impurities, since no direct measurements of neutral gas densities in sub-divertor and pump chamber are available and entrainment of impurities in the D 2 flow has to be considered. To shed some light on this, and to obtain a more realistic estimate of the impurity pumping, calculations with the divertor gas simulator (DIVGAS) code [15] were done in a simplified geometry.…”

“…The DIVGAS code has been proved to be a reliable tool for the modeling of the neutral gas dynamics in the particle exhaust of tokamaks and stellarators in recent years [15,[26][27][28]. DIVGAS is a particle-based code, and its main kernel is based on the stochastic direct simulation Monte Carlo (DSMC) method proposed by G. A. Bird in 1963 [29] aiming in solving numerically the Boltzmann equation.…”

Numerical simulation of neutral gas dynamics in the W7-X sub-divertor

“…For validation purposes, the DIVGAS code has already been implemented to model the neutral gas flow in the JET sub-divertor [5,6]. Moreover, DIVGAS has been applied for simulating the particle exhaust of ITER [7], JT60SA [8], EU-DEMO [9][10][11][12][13][14][15] and recently DTT [16] tokamaks.…”