L–H Transition

The sudden jump from low- to high-confinement mode above a power threshold.

Above a heating-power threshold, a plasma spontaneously transitions from L-mode to the roughly-doubled confinement of H-mode. Reaching the threshold is a design consideration for the breeder's heating.

Above a heating-power threshold the plasma spontaneously jumps to the roughly-doubled confinement of H-mode, so a machine's heating must comfortably exceed that threshold to operate in the high-confinement regime. The transition is one of fusion's most consequential empirical discoveries and underlies the confinement Kronos assumes.