Plasma wall interaction and plasma edge properties with radiation cooling and improved confinement in TEXTOR-94

The Radiative Improved Mode obtained on the limiter tokamak TEXTOR-94 combi nes power exhaust by a radiating plasma boundary with improved energy confi nement (as good as in the ELM-free H-mode in divertor tokamaks) at high pla sma densities (equal to or even above the Greenwald density) in quasi-stati onary discharges. Substantial changes of the plasma edge properties are obs erved with increasing radiation: a reduction of the plasma edge density and temperature, a reduction of particle transport out of the confined plasma volume and an increase of the penetration depth and of the fueling efficien cy of neutrals. In addition to an increased inward drift this causes a stee pening of the density profiles. For a given plasma current and heating scen ario the transition to improved confinement takes place as soon as the dens ity peaking reaches a critical threshold. With the injection of neon an inc reased sputtering yield of carbon and in addition photon induced desorption of oxygen from the wall are observed, leading to an increased dilution at the plasma edge, whereas the central dilution is only weakly affected. (C) 1999 Elsevier Science B.V. All rights reserved.