Physics of stimulated L-H transition

Miki, Kazuhiro

A central issue in H-mode physics is to achieve control, not only understanding. Control of the L-H transition is desirable, on account of the successful fusion power plants. We here report on model studies of stimulated L-H transitions. We have developed a one-dimensional mesoscale model. Numerical studies reveal that L-H transitions can be triggered by particle injection into a subcritical state. Particle injection alters the edge mean flow shear. For low ambient heating, strong injection is predicted to trigger a transient turbulence collapse. We predict that repetitive injection at a period less than the lifetime of the collapsed state can thus maintain the turbulence collapse and so sustain a driven H-mode-like state. We also observe that zonal flows do not play a critical role in stimulated transitions.