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 ExB shear is large. (author)