High-confinement mode (H-mode)

H-mode

An operating regime of magnetic confinement devices, mostly tokamaks, entered when the heating power passes a threshold. A thin layer at the plasma edge suddenly suppresses turbulence, building a steep step in pressure called the pedestal, and the plasma holds its heat roughly twice as well as in L-mode on the same machine. It was first reported on the ASDEX tokamak in Germany in 1982 (Wagner and colleagues, Physical Review Letters). H-mode is the baseline operating mode for ITER and most large tokamak designs. It has a cost: the steep edge collapses repeatedly in bursts called edge-localised modes (ELMs), which throw heat and particles onto the wall and must be controlled in a reactor. A plasma described as a long 'high-confinement' plasma is being described by its operating mode and its duration; its energy confinement time is still typically a second or less.

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