• Keränen, Kimmo
• Wang, Minqiang
• Aikio, Mauri
• Heikkinen, Veli

Abstract

A viewing system was designed and a prototype realized for the in-vesselinspection of the International Thermonuclear Experimental Reactor. Theviewing is based on the line scanning principle, and the system consists of 10identical units installed on top of the reactor at 36 deg intervals. Eachdevice contains a laser, beam steering mirrors, and viewing probe withinsertion mechanics. The probe has an outside diameter of 150 mm and a lengthof 14 m. The illumination design applies frequency-doubled Nd:YAG lasers whosebeams are guided through hermetically sealed windows into the vacuum vessel.The diffuser optics creates a vertically oriented light stripe onto the vesselsurface that is viewed by the imaging optics, consisting of 16 modulesaltogether covering horizontal and vertical field-of-views of 2 and 162degrees. The optical images are transferred to CCD cameras via coherent fiberarrays. The multi-focus design uses stacked fiber rows whose ends areassembled into different axial positions. The viewing probes rotate at aconstant angular speed of 1deg/s and pictures are taken at 0.01 deg intervals.The complete picture of the vessel interior is generated in 6 minutesproducing 5.8 *10 exp(9) image pixels. The image processing and analysis ofpossible defects in the vessel surfaces are performed off-line after theviewing procedure. A full-scale prototype of the viewing probe was constructedto demonstrate the feasibility of the design. Its illumination opticsutilizes a diffractive optics element that transforms the collimated inputbeam into a rectangular output lobe with uniform intensity. The prototype hashorizontal and vertical imaging optics field-of-views of 2 and 12 degrees. Thetest results showed that the prototype can take pictures of good qualityapplying a continuously rotating probe having an angular speed of 0.08 deg/s.In optimum conditions, the minimum resolvable feature size at 3-m distance issmaller than 1 mm, which satisfies the requirement specification. Furtherdevelopment is needed to increase the illumination power to improve theimaging speed and to develop linear fiber arrays that are compatible with thevacuum and high-flux radiation environment of the primary vacuum vessel.

Topics

• impedance spectroscopy
• surface
• defect