A new tokamak confinement regime has been observed on the Tokamak Fusion Test Reactor (TFTR) where particle and ion thermal diffusivities drop precipitously by a factor of ∼40 to the neoclassical level for the particles and to much less than the neoclassical value for the ions in the region with reversed shear. This enhanced reversed shear confinement mode allows the central electron density to rise from 0.45 × ${10}^{20}$ ${\mathrm{m}}^{-3\mathrm{}}$ to ∼1.2 × ${10}^{20}$ ${\mathrm{m}}^{-3\mathrm{}}$ with $T_i\sim 24$ keV and $T_e\sim 8$ keV. This regime holds promise for significantly improved tokamak performance.

• Received 23 May 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.4417