High-confinement mode


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 in 2016.

History

Prior to the H-mode’s discovery, all tokamaks operated in what is now called the or low-confinement mode. The 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 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 and the old lower confinement state was in turn called the Due to its improved confinement properties, quickly became the desired operating regime for most tokamak reactor designs.