JOREK predictive simulation for boron pellet fueling in the EHL-2 spherical torus

Boron (11B) pellet injection is designated as a routine fueling technique for the EHL-2 spherical torus. The predictive modelling of 11B pellet injection for H-mode plasma fueling in EHL-2 has been performed using the three-dimensional (3D) nonlinear magnetohydrodynamic (MHD) code JOREK. The simulation results show that the 11B pellet induces rapid local cooling and temperature profile contraction. This constrains the ablation rate to a relatively low level, enabling effective penetration through the pedestal region and injection into the core up to a position of 0.35 in the normalized poloidal flux. After the pellet is completely ablated, about 90% of the 11B can be deposited inside the separatrix. The increased edge resistivity from temperature contraction modifies the poloidal magnetic flux via Ampère's law. This perturbs the toroidal current density near rational surfaces, enhances the radial gradient there and drives multiple tearing modes. Interactions among high poloidal mode (high-m) edge magnetic islands lead to magnetic stochasticity, but the stochastic layer does not expand inward beyond the pedestal during injection. Post-complete ablation, tearing mode growth ceases, suggesting pellet injection can deliver material deeply without triggering persistently growing MHD instabilities.