Edge-Localized Modes (ELMs)

ELMs are violent edge instabilities that can destroy plasma-facing hardware. Kronos avoids them entirely with an ELM-free negative-triangularity edge.

What

Periodic bursts of energy from the plasma edge

Danger

Tens of MJ in sub-ms bursts; lethal to DEC grids

Companion of

H-mode (positive-triangularity operation)

Kronos answer

ELM-free negative-triangularity edge

Edge-Localized Modes (ELMs) are repetitive instabilities at the boundary of a high-confinement (H-mode) plasma. Each ELM flings a burst of particles and energy at the wall — a large one can deliver tens of megajoules in under a millisecond. For conventional reactors ELMs are a wall-erosion problem; for a machine with electrostatic direct-energy-conversion grids they are catastrophic.

Kronos sidesteps the problem entirely. The negative-triangularity edge is ELM-free by demonstrated regime physics, running an L-mode-like edge while keeping H-mode-grade core confinement. This is why δ = −0.30 is treated as a conserved invariant: the ELM-free edge is what makes direct energy conversion survivable.