An improved approach to eliminate the error induced by vibrations for laser speckle interferometry under tokamak vibrational environments

Abstract

To build an online and non-contact diagnosis system of surface morphology of Plasma-Facing Components (PFCs) in fusion devices, a measurement system based on Laser Speckle Interferometry (LSI) is in development in our laboratory. To preserve high resolution, the temporal phase-shifting technique which is sensitive to vibration was introduced. Considering that periodic vibration of the tokamak device will cause the phase shift which is not equal to the special constant value in each step, which will lead to the distortion of the reconstructed surface. In this paper, we introduced an improved phase distribution extraction approach based on Least-square iteration to deal with the vibrational effect. In the process of phase extraction, we combined the amount of phase shift and the phase introduced by vibration together and treated them as an unknown parameter. Then the amount of phase-shifts and the phase distribution could be determined by means of the iteration process. Benchmark tests were conducted on Tungsten (W) material which related to PFCs. A laser ablation method was used to simulate the erosion process during the Plasma-Wall Interaction (PWI) of the tokamak environment. Results show that the morphology results measured by the Least-square iteration approach is very close to the measurement results from the confocal microscopy with the relative error rates within 20%. This indicates that the LSI measurement system based on the Least-square iteration approach is promising for real-time online monitoring in Experimental Advanced Superconducting Tokamak (EAST) vibration environments.