Utilizing M3D-C¹ to understand triggering of ELMs in pellet pacing experiments in DIII-D ITER-like plasmas

Large edge localized modes (ELMs) in magnetically confined plasmas can lead to the sudden release of thermal and magnetic stored energy and can potentially cause damage to plasma facing components, especially as stored energy increases in larger devices. ELM pacing via injection of hydrogenic pellets can trigger small ELMs at a rate exceeding the natural ELM frequency and has been shown to be a successful method to mitigate effects of large ELMs. Understanding of the physical mechanisms of ELM triggering and improved modeling are required for confident extrapolation to ITER and beyond. M3D-C¹, a code for solving the linear or non-linear extended-MHD equations in toroidal geometry, is currently being used to model pellet ELM triggering in DIII-D ITER-like plasmas. An unstructured triangular mesh provides resolution to capture the sharp gradients present in the pellet deposition layer. Initial linear results utilizing a density perturbation to estimate the effects of the pellet in 2D suggest that the destabilization is a resistive effect. Recent M3D-C¹ modeling efforts have focused on 3D nonlinear simulations incorporating a pellet ablation model.