MICROTURBULENCE REDUCTION DURING NEGATIVE CENTRAL SHEAR TOKAMAK DISCHARGES

Increased temperature, confinement, and fusion reactivity recently ach ieved during discharges in the DIII-D Tokamak [J. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International A tomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] with negative cent ral magnetic shear (NCS) are accompanied by reduced core electrostatic microturbulence. Comparison of fluctuation characteristics between di scharges with and without NCS reveals significant differences in the l evel and location of microturbulence. While the cause, or instability, for the microturbulence is not known, the reduction of the saturated level is consistent with models incorporating negative shear stabiliza tion and turbulence stabilization by sheared EXB flow. (C) 1997 Americ an Institute of Physics. [S1070-664X(97)00511-9].