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 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, N=aBI, up to 4 (%-m-T/MA), energy confinement are a factor of 3 better than L mode, and at least 50% of the noninductive plasma current in this regime demonstrates compatibility with requirements for a steady-state high-beta tokamak power plant.