Enhanced confinement and stability in DIII-D discharges with reversed magnetic shear

Peaked pressure profiles and central ion temperatures up to 20 keV are observed in DIII-D {ital H}-mode discharges with a central region of strongly reversed magnetic shear. Short wavelength ballooning modes are stabilized by access to the second stable regime, longer wavelength modes by a conducting wall and possibly by rotational shear. Values of normalized beta, {beta}{sub {ital N}}={beta}{ital aB}/{ital I}, up to 4 ({percent}-{ital m}-T/MA), energy confinement are a factor of 3 better than {ital L} mode, and at least 50{percent} of the noninductive plasma current in this regime demonstrates compatibility with requirements for a steady-state high-beta tokamak power plant. {copyright} {ital 1995 The American Physical Society.}