Wide-angle visible video diagnostics for JT-60SA utilizing EDICAM

A multi-purpose, wide-angle, visible overview video diagnostic, based on the EDICAM camera, was designed for JT-60SA superconducting tokamak, in order to fulfill both machine protection and scientific observation purposes. The detector is located inside the ‘port plug’ (a ca. 3 m long re-entrant tube), relatively close to the plasma boundary; the EDICAM can tolerate the magnetic field at this location as well as the radiation levels in the early phases of the experiment. A rail-and-carriage system is used to move the detector between the opening of the port plug and the measurement location. A 4-point docking system ensures the precise and robust positioning of the optics, firmly holding the detector also in the event of disruptions or earthquakes. The camera is running under atmospheric condition, separated by a sapphire window from the plasma vacuum. The vacuum window is protected by a water-cooled pin-hole from mechanical impacts and plasma heat; the pin-hole is also the first element of the detector’s optical system. The optics consists of two lens groups and a prism; the housing is made of stainless steel, in order to reduce eddy currents and thus avoid large forces acting on the system in a disruption.