Upgraded bolometer system on JET for improved radiation measurements

Two new main-vessel bolometric cameras (KB5) with horizontal and vertical views of the plasma cross-section have been installed on JET, providing a substantial upgrade in capabilities: more viewing chords (24 chords for each camera), higher energy range (up to 8 keV), higher sensitivity (∼6.2 V/W), lower noise and therefore, lower detectable signals (∼2 μW/cm2 at a bandwidth of 200 Hz), higher temporal resolution (∼2 ms). In addition, three new dedicated divertor bolometer cameras (KB3) with 12 lines-of-sight in total, optimised views and technical improvements have replaced the old ones. The combination of KB3 and KB5 systems provides measurements with significantly improved spatial resolution, allowing the divertor and main chamber radiation fractions to be clearly resolved. The sensitivity measured with an in situ electrical method matches very well with that obtained using a light source calibration. The deviation between the two methods is less than 7% and is in the range of the measurement accuracy. The experimentally measured geometric functions closely match those computed using the design values of geometry. Tomographic reconstructions of high density divertor plasmas with ITER-like configuration are presented which clearly demonstrate the capability of the new diagnostic.