Transport and improved confinement in high power edge radiation cooling experiments on TEXTOR

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Abstract
A stationary high level of edge radiation ( gamma =Prad/Ptot up to ~90% with peak radiation up to ~1 MW/m3) has been obtained in TEXTOR by using silicon and/or neon as radiating impurities. The confinement and neutron reactivity are not degraded but can even be improved at high plasma densities. Stationary reactor relevant heating and radiated power flows with a figure of merit fH/qa=0.6 have been achieved. The interpretation of these results shows a reduction of the bulk transport in the presence of edge radiation cooling. The properties of the radiatively cooled discharges are interpreted or modelled mainly by the self-consistent radiative transport code RITM, and also by the codes TRANS and PRETOR. From these modelling studies an enhancement of the bulk confinement is found in terms of the reduction of the convective losses and the decrease of the edge electron temperature, which results in a peaking of the current profile. The code RITM also predicts self-consistently the detailed properties of the radiating layer for different injected impurities as a function of their incoming flux, and shows that the optimal conditions to obtain confinement improvement as well as minimum fuel dilution by the radiating impurity are obtained at high density