Regime of very high confinement in the boronized DIII-D tokamak

Abstract

Following boronization, tokamak discharges in DIII-D have been obtained with confinement times up to a factor of 3.5 above the ITER89-P L-mode scaling and 1.8 times greater than the DIII-D/JET H-mode scaling relation. Very high confinement phases are characterized by relatively high central density with ${\mathit{n}}_{\mathit{e}}$(0)\ensuremath{\approxeq}1\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$, and central ion temperatures up to 13.6 keV at moderate plasma currents (1.6 MA) and heating powers (12.5--15.3 MW). These discharges exhibit a low fraction of radiated power, P\ensuremath{\le}25%, ${\mathit{Z}}_{\mathit{e}\mathit{f}\mathit{f}}$(0) close to unity, and lower impurity influxes than comparable DIII-D discharges before boronization.