Speckle interferometry diagnostic for erosion/redeposition measurements in tokamaks

In order to measure erosion/redeposition during long duration discharges, a new diagnostic based on speckle interferometry is proposed. First experiments performed on carbon fiber composite materials have shown that this technique is able to measure a modification of the surface in the range of 1 μm. Further experiments have been performed on different materials using a second wavelength in order to increase the dynamic range from 0.1 to 100 μm and to perform 3D measurements of the surface. A diagnostic based on two-wavelength speckle interferometry to measure in situ erosion/redeposition during a single discharge on the CIEL limiter is under development.