Performance of the BGSDC integrator for computing fast ion trajectories in nuclear fusion reactors

Krasymyr Tretiak,James Buchanan,Rob Akers,Daniel Ruprecht

doi:10.1016/j.cpc.2021.107876

Abstract

Modelling neutral beam injection (NBI) in fusion reactors requires computing the trajectories of large ensembles of particles. Slowing down times of up to one second combined with nanosecond time steps make these simulations computationally very costly. This paper explores the performance of BGSDC, a new numerical time stepping method, for tracking ions generated by NBI in the DIII-D and JET reactors. BGSDC is a high-order generalization of the Boris method, combining it with spectral deferred corrections and the Generalized Minimal Residual method GMRES. Without collision modelling, where numerical drift can be quantified accurately, we find that BGSDC can deliver higher quality particle distributions than the standard Boris integrator at comparable computational cost or comparable distributions at lower computational cost. With collision models, quantifying accuracy is difficult but we show that BGSDC produces stable distributions at larger time steps than Boris.

Highlights

Computer simulations are a critical tool for the design and operation of fusion reactors [1]
We show that BGSDC delivers better distributions with smaller mean and standard deviation than Boris and, if means and standard deviations of the order of micrometres are desired, can deliver them with less computational work
We compare the performance of the BGSDC time stepping algorithm against the standard Boris integrator when computing trajectories of fast ions generated by neutral beam injection into a fusion reactor

Summary

Introduction

Computer simulations are a critical tool for the design and operation of fusion reactors [1]. Numerical computation of the trajectories of fast ions generated, for example, from neutral beam injection is important to minimize wall loads and energy loss from ions escaping magnetic confinement [2]. At their core, particle trackers integrate the Lorentz equations x(t) = v(t).

Methods

Results

Conclusion