Internal transport barriers in FTU at ITER relevant plasma density with pure electron heating and current drive

FTU significantly contributes to study ITER-relevant internal transport barriers (ITB), which require steadiness, high plasma density (n-bare ≥1020 m-3), dominant electron heating and negligible momentum input. Its two radiofrequency systems, lower hybrid (LH, up to 1.9 MW at 8 GHz) and electron cyclotron (EC, up to 1.5 MW at 140 GHz), form and sustain steadily ITBs all along the heating pulse, >35τE, and ∼τR/L at ne0>1.3·1020 m-3 and Te0∼5.5 keV (τE=energy confinement time, τR/L=ohmic current relaxation time, ne0 and Te0=central density and electron temperature). Almost full current drive (CD) conditions are maintained with τE improved up to 1.6·τE,ITER97-L. The proper safety factor profile q(r), almost flat or slightly reversed in the core (qmin∼1.3) is established by off-axis LH-CD with important contribution of off-axis EC-CD or central counter ECCD. ITB radii rITB/a up to 0.67, and steadily up to =0.6 are obtained, by controlling the LHCD deposition profile. Peripheral LHCD is favored by lower q, and, at less extent, by broader Te(r) in turn established by off-axis EC heating. Good alignment of the bootstrap current is always obtained, with Ib/Ip up to 30%. The ITB strength is controlled by EC heating inside the barrier. Turbulence close to the ITB radius is depressed consistently with the improved confinement. Significant collisional ion heating inside the ITB (ΔTi0/Ti0≥35%, but still far from thermal equilibrium with electrons) and the almost neoclassical value of the ion transport indicate that e--i+ collisions do not affect the barrier dynamics. An anomalous inward particle pinch also at high density permits peaked profiles, ne0/∼1.7, in full CD plasmas despite the absence of the neoclassical Ware pinch. (author)