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 (≃ 1020mγ--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> Pohthe 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. © 2001 Published by Elsevier Science B.V.
All Science Journal Classification (ASJC) codes
- Civil and Structural Engineering
- Materials Science(all)
- Nuclear Energy and Engineering
- Mechanical Engineering