Influence of Plasma and Machine Parameters on Time to First ELM in DIII-D

Feature selection via multilinear regression is performed on 506 H-mode discharges on DIII-D, highlighting the parameters most influential on the timing of the first edge-localized-mode (ELM) event after an L-H transition. This database study illuminates key parameters that can be used to delay the advent of ELMs after entering H-mode, extending the window for establishing ELM-suppression via resonant magnetic perturbations (RMPs) to avoid damaging plasma-facing components in ITER or future fusion reactors. Database time-to-first-ELM in DIII-D ranged from <10 ms to 1200 ms, and all discharges using RMP or no-ELM regimes were excluded. Results show linear correlations between poloidal beta and ohmic power sampled at the L-H transition and the time-to-first-ELM, especially in discharge subgroups with similar triangularity. Increased plasma pressure at the L-H transition and the strength of the plasma shape appear to influence the time-to-first-ELM. This investigation will be further generalized with additional machines in an effort to avoid systematic errors and provide suggestions for optimizing RMP application before the first ELM in future devices.