ELECTRON THERMAL TRANSPORT BARRIER AND MAGNETOHYDRODYNAMIC ACTIVITY OBSERVED IN TOKAMAK PLASMAS WITH NEGATIVE CENTRAL SHEAR

In the Rijnhuizen Tokamak Project, plasmas with steady-state negative central shear (NCS) are made with off-axis electron cyclotron heating. Shifting the power deposition by 2 mm results in a sharp transition o f confinement. The good confinement branch features a transport barrie r at the off-axis minimum of the safety factor (q), where q less than or equal to 3, and two magnetohydrodynamic (MHD) instabilities, where one is localized at the off-axis minimum of q and one covers the entir e NCS region. The low confinement branch has q > 3 everywhere, no tran sport barrier, and no MHD activity.