Design study of a wide-angle infrared thermography and visible observation diagnostic on JT-60SA

Design study of a wide-angle infrared (IR) thermography (surface temperature measurement) and visible observation diagnostics for JT-60SA are reported. The new design offers an optical solution without a “blind spot” which is one of the advantages. In order to image a large section inside the vacuum vessel (both in poloidal and toroidal directions), the optical system of endoscope is to provide a wide-angle view in the IR and visible wavelength ranges. The estimated IR optical spatial resolution is approximately 2 cm at a distance of 7.6 m from the front optics with a pupil diameter of 4 mm. For a surface temperature measurement it would be larger (∼4 cm for a surface temperature error less than 5%). The optics of this system can be divided into three parts: (1) a mirror based optical head (two set of spherical mirrors plus two flat mirrors) that produces an intermediate image, (2) a Cassegrain telescope system, and (3) a relay group of lenses, being adapted to the two kinds of detectors for IR and visible observations.