Exploring 3D effects in runaway electron impacts in SPARC

Runaway electrons (REs) can pose dangers to tokamak plasma facing components (PFCs) due to their ability to deposit large amounts of energy onto localized wetted areas. In future experiments such as SPARC¹, individual REs can carry 10s of MeV of energy and RE beams can carry MAs of current and 10s of MJ of total energy. This work explores the 3D dynamics of runaway electron (RE) impacts in SPARC to better understand the damage they can cause. The HEAT² RE module is used to study an M3D-C1³ simulation of RE loss due to field stochastization. In this simulation, 2.5 MA of RE current is lost over the course of a few ms. HEAT is used to calculate the footprint and heat flux in this scenario as well as to estimate the temperature rise in PFC components. 3D CAD is used to explore the dynamics between 3D fields and realistic PFC geometries. We also explore the effect of PFC misalignment on impact wetted areas. We find that assembly misalignments of the vacuum vessel cause much larger toroidal footprint asymmetries than individual tile misalignments.

¹Creely et al. (2020). Overview of the SPARC tokamak. Journal of Plasma Physics, 86(5), 865860502. https://doi.org/10.1017/S0022377820001257

² Looby et al. (2022). A Software Package for Plasma-Facing Component Analysis and Design: The Heat Flux Engineering Analysis Toolkit (HEAT). Fusion Science and Technology, 78(1), 10–27. https://doi.org/10.1080/15361055.2021.1951532

³Ferraro et al. (2016). Multi-region approach to free-boundary three-dimensional tokamak equilibria and resistive wall instabilities. Physics of Plasmas, 23(5), 056114. https://doi.org/10.1063/1.4948722