Improved radiation measurements on JET – First results from an upgraded bolometer system

To improve the quality of radiation measurements, two new bolometric cameras with horizontal and vertical views of the plasma cross-section have been installed on JET. These cameras provide measurements with significantly improved spatial resolution, allowing the divertor and main chamber radiation fractions to be clearly resolved. Analysis of radiation profiles under attached and detached divertor conditions as well during the formation of an X-point MARFE (XPM) close to an ohmic density limit are presented. The radiation power fraction γ = Prad/Pheat increases from 0.5 to 0.8 just before XPM onset. A large fraction of this radiation is located in the divertor (Praddiv/Pradtot=0.56 at low density and about 0.67 at XPM onset). In addition, spatial distributions of radiation in recent ITER-like configuration discharges are presented.