Confinement and turbulence study in the Frascati Tokamak Upgrade high field and high density plasmas

The Frascati Tokamak Upgrade (FTU) is a high field and high density device which allows one to study confinement and transport at plasma parameters generally not accessible to other tokamaks and is relevant to next generation experiments (ITER). In this paper we study the effect of different density, temperature and q profiles on confinement and transport in various types of plasmas including ohmic, externally heated and pellet-fuelled discharges. Peaking of the electron density profile in pellet-fuelled discharges has been found to enhance the energy confinement time on FTU to values as high as 120 ms at densities of the order of those expected in ITER. Experiments designed to further improve confinement by injecting pellets at higher densities show the existence of a second threshold for saturation of confinement when the local electron heat conductivity corresponds to the same order of the local ion neoclassical conductivity in the region of maximum temperature gradient. Reflectometry measurements show turbulence suppression in pellet-injected discharges (as predicted by microstability analysis) and give insights to the change in turbulence in electron internal transport barrier plasmas. Finally, particle transport has been studied in experiments with full LH current drive.