High-confinement mode, or H-mode, is an operating mode possible in toroidal magnetic confinement fusion devices – mostly tokamaks, but also in stellarators. In this mode the plasma is more stable and better confined.
It was discovered by Friedrich Wagner in 1982 during neutral-beam heating of the plasma at ASDEX. It has since been reproduced in all major toroidal confinement devices and is planned in the operation of ITER. Its self-consistent theoretical description was a topic of research in 2007. It was still considered a mystery with multiple competing theories (e.g. predator–prey model) in 2016.
Prior to the H-mode’s discovery, all tokamaks operated in what is now called the L-mode, or low-confinement mode. The L-mode is characterized by relatively large amounts of turbulence, which allows energy to escape the confined plasma. Moreover, it was observed that as the heating power applied to an L-mode plasma increased, the confinement decreased. However, it was discovered in 1982 on the ASDEX tokamak that if the heating power applied using neutral beams was increased beyond a certain critical value, then the plasma spontaneously transitioned into a higher-confinement state. This new state was called the H-mode, and the old lower-confinement state was in turn called the L-mode. Due to its improved confinement properties, H-mode quickly became the desired operating regime for most tokamak reactor designs.
- Edge-localized mode, an instability of H-mode
- Joint European Torus (JET) operates in H-mode
- COMPASS tokamak can/could operate in H-mode
- KSTAR (South Korea) operates in H-mode
- EAST (China) operates in H-mode
- NSTX-U operates in H-mode