TRANSPORT AND IMPROVED CONFINEMENT IN HIGH-POWER EDGE RADIATION COOLING EXPERIMENTS ON TEXTOR

A stationary high level of edge radiation (gamma = P-rad/P-tot up to s imilar to 90% with peak radiation up to similar to 1 MW/m(3)) has been obtained in TEXTOR by using silicon and/or neon as radiating impuriti es. The confinement and neutron reactivity are not degraded but can ev en be improved at high plasma densities. Stationary reactor relevant h eating and radiated power hows with a figure of merit f(H)/q(a) = 0.6 have been achieved. The interpretation of these results shows a reduct ion of the bulk transport in the presence of edge radiation cooling. T he properties of the radiatively cooled discharges are interpreted or modelled mainly by the self-consistent radiative transport code RITM, and also by the codes TRANSP and PRETOR. From these modelling studies an enhancement of the bulk confinement is found in terms of the reduct ion of the convective losses and the decrease of the edge electron tem perature, which results in a peaking of the current profile. The code RITM also predicts self-consistently the detailed properties of the ra diating layer for different injected impurities as a function of their incoming flux, and shows that the optimal conditions to obtain confin ement improvement as well as minimum fuel dilution by the radiating im purity are obtained at high density.