Physics of and achievements with the H-mode

The H-mode is a confinement mode of toroidal plasmas which may make the goals of fusion possible - the development of a clean energy source at competitive electricity costs. The most challenging aspect in the understanding of the H-mode physics is the sudden disappearance of the edge turbulence whereas its potential driving forces increase. As the physics behind the H-mode is subtle many features are not yet clarified. There is, however, substantial experimental and theoretical evidence that turbulent flows, which normally limit the confinement, are diminished by sheared poloidal flow residing at the plasma edge. There are many potential mechanisms giving rise to sheared flow. The most intriguing of these is that fluctuations themselves induce the flow, which acts back to its generating origin and annihilates the turbulence. This review summarizes some of the studies on and achievements with the H-mode both for tokamaks and stellarators.