High Core Electron Confinement Regimes in FTU Plasmas with Low- or Reversed-Magnetic Shear and High Power Density Electron-Cyclotron-Resonance Heating

Electron temperatures in excess of 8 keV have been obtained by electron-cyclotron-resonance heating on FTU plasmas at peak densities up to $8\times {10}^{19}\mathrm{m}{}^{-3\mathrm{}}$. The magnetic shear in the plasma core is low or negative, and the electron heat diffusivity remains at, or below, the Ohmic level $(0.2\mathrm{m}{}^2/\mathrm{s})$, in spite of the very large heating power density $(10–20\mathrm{MW}/\mathrm{m}{}^3)$ which produces extremely high temperature gradients (up to 120 keV/m). The ion heat transport remains at the neoclassical level.