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 $8\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{m}{}^{\ensuremath{-}3}$. 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.