Dependence of the low to high confinement mode transition power threshold and turbulence flow shear on injected torque

The power required to induce a bifurcation from a low-confinement mode to a high-confinement mode in DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] plasmas is found to depend sensitively on the injected neutral beam torque and consequent toroidal rotation. Plasmas exhibit a factor of 2–4 reduction in this power threshold, dependent on ion ∇B drift direction. Correlated with this change, turbulence velocity measurements near 0.9<r/a<1.0 for balanced injection demonstrate significantly larger poloidal flow shear at a given injection power, relative to cocurrent injection, facilitating the confinement transition.