Microturbulence reduction during internal transport barrier discharges in DIII-D

Increased plasma confinement, temperature and fusion reactivity in negative central shear (NCS) discharges in DIII-D are accompanied by reduced core electrostatic microturbulence. The microturbulence reduces as the local radial electric field and shear increases, consistent with a theoretical model incorporating turbulence stabilization by shear radial electric field. Reduced turbulence and the associated anomalous transport reduction leads to further increased radial electric field shear via a steeper pressure gradient and reduced momentum transport. During the H-mode phase of a core transport barrier discharge, the microturbulence is virtually quenched in the core. Increasing evidence indicates that the transport barrier initially forms in the plasma interior when E x B shear is large.