Confinement improvement mechanism in very high mode (VH mode)

The mechanism for confinement improvement in the toroidal-rotation-induced very high mode (VH mode) may be the turbulence suppression due to the shear of the toroidal angular frequency associated with parallel flow. This explanation is in contrast to the plausible hypothesis that high-mode (H-mode) confinement improvement may be caused by the turbulence suppression due to the shear of the poloidal angular frequency associated with E×B and parallel flows. Here, E is the electric field and B is the magnetic field. A theory for VH mode, based on the rapid change of the radial gradient of the toroidal flow, is presented.