High-confinement mode

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High-confinement mode, or H-mode, is an operating mode possible in toroidal magnetic confinement fusion devices – mostly tokamaks, but also in stellarators.[1] 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.[1] 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.[2] It was still considered a mystery with multiple competing theories (e.g. predator–prey model) in 2016.[3]


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.[1] 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.

See also[edit]


  1. ^ a b c How Fritz Wagner "discovered" the H-Mode.
  2. ^ F. Wagner (2007). "A quarter-century of H-mode studies". Plasma Physics and Controlled Fusion. 49 (12B): B1. Bibcode:2007PPCF...49....1W. doi:10.1088/0741-3335/49/12B/S01.
  3. ^ First results of NSTX-U research operations presented. Oct 2016.