Challenges and opportunities in exascale fusion simulations

The challenging computational requirements of nuclear fusion research arise from the multiple timescales and space scales involved in the physics and engineering processes of a fusion device. Owing to the intrinsic and complex interconnections of these processes, the complex multiphysics and multiscale nature of fusion simulations require the capabilities of cutting-edge supercomputers. Advances in supercomputing enable a move towards larger-scale, higher-fidelity full fusion reactor digital models that capture not only the plasma core and edge physics but also interactions with materials and engineering aspects, such as fusion reactor walls and cooling systems. This Perspective discusses the main opportunities that fusion codes face in the transition to the emerging exascale systems and beyond, and the challenges that remain to be overcome. This Perspective provides a brief, opinionated review of the past, present and future of the convergence between supercomputing and fusion simulations. We discuss the progress that has been made, the challenges that have been overcome and those that remain as we move into the post-exascale era.