Edge-Localised Modes (ELMs)

Periodic bursts of energy from the plasma edge that can erode plasma-facing components.

H-mode's edge barrier stores energy that is periodically expelled in bursts called ELMs. Large ELMs deposit heat on the divertor and first wall in ways that can shorten component life.

HYPERION's negative triangularity (δ = -0.30) is chosen in part to suppress ELMs — a real, physics-based benefit rather than an add-on control system.

ELMs are the price of the H-mode pedestal: the stored edge energy is expelled in periodic bursts that erode the divertor and first wall. Large machines invest heavily in ELM control. HYPERION's negative triangularity is chosen partly to suppress them passively, easing one of the toughest lifetime problems in tokamaks.