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 8×10¹⁹m^-3. The magnetic shear in the plasma core is low or negative, and the electron heat diffusivity remains at, or below, the Ohmic level (0.2m²/s), in spite of the very large heating power density (10--20MW/m³) which produces extremely high temperature gradients (up to 120 keV/m). The ion heat transport remains at the neoclassical level.