Author/Authors :
Cirant، نويسنده , , S and Airoldi، نويسنده , , A and Bertalot، نويسنده , , L and Bruschi، نويسنده , , A and Bracco، نويسنده , , G and Buratti، نويسنده , , P and Cenacchi، نويسنده , , G and Esposito، نويسنده , , B and Granucci، نويسنده , , L. and Kroegler، نويسنده , , H and Lazzaro، نويسنده , , E and Nowak، نويسنده , , S and Ramponi، نويسنده , , G and Sozzi، نويسنده , , C and Tudisco، نويسنده , , O and Zerbini، نويسنده , , M and Group، نويسنده , , IFP and Team، نويسنده , , FTU، نويسنده ,
Abstract :
Plasma absorption at the fundamental EC resonance of e.m. waves at 140 GHz, 0.8 MW, Ordinary mode, provides in the FTU tokamak a localized (minimum δr ≃2.5 cm) and intense (up to ≃100 MW/m3) heat source for the electrons. It is shown that at high density (≃1020 mγ−-3) ions are heated (ΔTi/Ti=0.25) by collisional e−i energy transfer and assuming ion thermal diffusivity about three times larger (at most) than predictions in order to account for the observed Ti. Off-center localization (rabs/a ≃0.2) of the ECRH heat source changes the electron temperature (and current density) profile in a way to fully stabilize sawteeth. On-axis absorption accelerates the sawtooth crash repetition rate if Pecrh⩽Poh, but with Pecrh>Poh the sawtooth period is increased. A critical shear model for the sawtooth crash repetition rate is shown to be in agreement with its experimental dependence on resonance position and heating power. In discharges characterized by a flat temperature profile in the ohmic phase, ECRH may de-stabilize tearing modes of different order, with a strong degradation of core energy confinement.
