CORE FLOW SHEAR AS THE CAUSE OF VERY HIGH CONFINEMENT IN THE DIII-D TOKAMAK

The leading hypothesis for the cause of the very high confinement obse rved during VH mode in DIII-D is that a spontaneous increase in the co re flow shear suppresses microturbulence which reduces transport loss and, for example, further increases flow, in a positive feedback cycle . This is confirmed by using 'magnetic braking' as an independent cont rol of the toroidal rotation contribution to the flow; when the toroid al rotation shear of a VH mode discharge is reduced, the turbulence an d transport increase back to the level observed during 'standard' H mo de.