H-mode and L-mode

H-mode is a high-confinement regime with a dangerous edge; L-mode is quieter but leakier. Kronos uses negative triangularity to get the best of both.

L-mode

Low confinement, quiet edge

H-mode

High confinement via an edge transport barrier — but ELMs

Kronos regime

L-mode-like edge, H-mode-grade core (NT)

Evidence

DIII-D 2023 NT campaign

Tokamak plasmas run in two broad confinement regimes. L-mode ("low") has a quiet, stable edge but leaks heat relatively easily. H-mode ("high") forms an edge transport barrier that roughly doubles confinement — but that barrier is what drives ELMs, the violent edge bursts that threaten plasma-facing hardware.

Most reactor designs accept H-mode and then fight its ELMs. Kronos takes a different route: negative triangularity delivers H-mode-grade core confinement with an L-mode-like edge — the quiet edge of L-mode and the good confinement of H-mode at once. The 2023 DIII-D campaign demonstrated exactly this combination (H₉₈,y2 ≥ 1, β_N > 2.5 with the L-mode edge intact).