Study of TEXTOR ICRF Antenna Coupling in the ICWC Mode of Operation

Ion Cyclotron Wall Conditioning (ICWC) discharges, in pulsed-mode operation, were carried out in TEXTOR to simulate a scenario of ITER wall conditioning at half-field. The ICWC discharges were performed in a continuous Helium flow with adjunction of molecular Hydrogen, puffed after the ICRF ignition thus achieving better antenna coupling in the Mode Conversion scenario with improved ICWC performance. Reproducible generation of ICRF plasmas and reliable wall conditioning, after proper wall preloading with Deuterium glow, were achieved by coupling the RF power at 29 MHz from one or two ICRF antennas at different toroidal magnetic fields (different cyclotron harmonics). The antenna coupling properties were analyzed in relation to wall conditioning output (removal rates) for selected marker masses. Present study of ICWC at low and high power density per particles (at different gas pressures) emphasizes on the efficiency of the application of stationary, oscillating or rotating poloidal magnetic field. These experimental results will be compared with the predictions of a 0-D RF plasma production model.