Demonstration of high performance negative central magnetic shear discharges on the DIII-D tokamak

摘要

Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L-mode, and high confinement, H-mode, regimes in the DIII-D tokamak. In the region of shear reversal, significant peaking of the toroidal rotation (f(sub phi) approx. 30-60 kHz) and ion temperature (T(sub i)(0) approx. 15-22 keV) profiles are observed. In high power discharges with an L-mode edge, peaked density profiles are also observed. Confinement enhancement factors up to H equivalent to tau(sub E)/tau(sub ITER-89P) approx. 2.5 with an L-mode edge, and H approx. 3.3 in an Edge Localized Mode (ELM)-free H-mode, are obtained. Transport analysis shows both ion thermal diffusivity and particle diffusivity to be near or below standard neoclassical values in the core. Large pressure peaking in L-mode leads to high disruptivity with Beta(sub N) equivalent to Beta(sub T)/(I/aB) <= 2.3, while broader pressure profiles in H-mode gives low disruptivity with Beta(sub N) <= 4.2.