JOREK simulations of edge-localized mode effects on heat load and target erosion in the EHL-2 spherical torus

This study utilizes the nonlinear magnetohydrodynamic code JOREK to investigate edge-localized mode (ELM) dynamics in the EHL-2 spherical torus, which is a device specifically designed for p-¹¹B fusion. The nonlinear evolution of multi-mode ELMs as well as their impact on divertor heat loads and target erosion have been investigated in detail. Nonlinear simulations that incorporate toroidal modes ranging from n = 2 to 20 unveil a mode transition process. Specifically, although linear analysis designates n = 18 as the most unstable mode, the nonlinear interactions result in the n = 16 mode becoming dominant during the crash phase. The ELM crash triggers stochastic magnetic fields, enhances cross-field transport, and causes the pedestal pressure to decrease by approximately 20%. Moreover, around 0.1 MJ of energy (10% of the total pedestal energy) is released into the scrape-off layer as a result of this crash. This leads to a significant heat flux that peaks at ∼80 MW/m2 on the outboard divertor targets. Further, the simulation result shows that the physical sputtering, dominates carbon erosion with peak erosion flux reaching 6.5×1021 m-2s-1. These findings highlight severe challenges for plasma-facing components and underscore the urgency of developing effective ELM control schemes for sustainable p-¹¹B operation in EHL-2.