Progress towards Internal Transport Barriers at High Plasma Density Sustained by Pure Electron Heating and Current Drive in the FTU Tokamak

Strong electron Internal Transport Barriers (ITB) are obtained in FTU by the combined injection of Lower Hybrid and Electron Cyclotron RF waves. ITBs occur either during the current plateau or during the ramp up phase, and both in full and partial current drive (CD) regimes. Central electron temperatures Te0 > 11 keV at central densities close to 0.8 . 1020m- 3 are sustained for several confinement times. The transport barrier is wider than r/a = 0.4 and slowly expands in time up to r/a = 0.4. It extends over a region where a slightly reversed magnetic shear is established by off-axis LH current drive. The EC power, instead, is used either to benefit from this improved confinement by heating inside the ITB, or to enhance the peripheral LH power deposition and CD with off axis resonance. Despite the fact that the very high Te0 reduces the e- to i+ energy transfer by 1.4 times during the ITB, the neutron yield is three times larger than in a reference ohmic discharge.