New bolometry cameras for the JET Enhanced Performance Phase

Two new bolometer cameras, for horizontal and vertical views of the plasma cross-section, are under construction for the Enhanced Performance Phase of JET, to begin in 2005. These cameras replace previous cameras in operation and represent a substantial upgrade in capabilities: more viewing chords over a larger viewing angle, higher detectable energy range, higher sensitivity, lower noise level and therefore, lower detectable signal (∼1 μW/cm2 for τ = 2 ms versus ∼70 μW/cm2 for τ = 20 ms). The detectors are essentially the same as those in use on ASDEX-Upgrade (gold energy-absorbing layer, mica substrate, gold meander), whereby the absorber layer has been increased in thickness from 4 to 8 μm in order to extend sensitivity to 8 keV. Each camera is comprised of 24 channels, with a particularly fine spatial resolution in the divertor region of ∼8 cm. Definition of the lines-of-sight is attained by a collimator arrangement for the vertical camera and use of pinholes for the horizontal camera. Salient design features of these cameras are described.