Feasibility study of digital holography for erosion measurements under extreme environmental conditions inside the International Thermonuclear Experimental Reactor tokamak [invited].

In the International Thermonuclear Experimental Reactor under construction in southern France, there will be a need for continuous measuring of the erosion at the wall, after the reactor starts operating. A two-wavelength interferometric technique based on digital holography is proposed for the erosion measurement. This technique has the ability to tackle the challenging environmental conditions within the reactor by a long-distance measurement, where a relay optic will be used for imaging the investigated surface on the detector. We will show that the shape measurements of objects located at a distance of more than 20 m from the measuring head can be carried out in a short time (100 µs) by the two-wavelength interferometric technique. A depth accuracy of ±10 µm is achieved.