Electron Cyclotron Resonance Heating on TEXTOR: results from the preliminary 110 GHz system

A 110 GHz, 400 kW, 200 ms gyrotron has been employed on TEXTOR for ECRH. The highly localised electron heating allowed the identification of (multiple) electron transport barriers. The RTP q-comb model for the electron heat conductivity gives a good description of TEXTOR results with ECRH in Ohmic discharges. Central ECRH in the current ramp phase speeds up central current penetration due to the highly peaked Te profile. A stable evolution of these discharges with early heating required the combination of counter-NBI with central ECRH. In RI-mode, central ECRH resulted in an increase of the confined energy in proportion to the ECRH power, without signs of power degradation as is usual in RI-mode with NBI and ICRH. Efficient ECRH is observed up to the X-mode cut-off density. The gyrotron has also been successfully used for diagnosis of energetic ions by means of Collective Thomson Scattering.