Study of microscale surface morphology changing of the retroreflector in EAST by means of laser speckle interferometry technique

Abstract

• The surface morphology of the retroreflector served in EAST is first time reconstructed through a 3D visual exhibition. • Three internal reflection planes of the retroreflector served in EAST appear severely different surface morphology features. • Laser speckle interferometry technique is a reliable surface morphology characterization approach for PFMs. The retroreflectors in EAST (Experimental Advanced Superconducting Tokamak) are important optical components of Polarimeter-Interferometer (POINT) system, working as the first mirrors to reflect the incident far-infrared laser. The surface morphology changing of the retroreflector has a direct impact on the optical reflection accuracy and it will generate a significant influence on EAST plasma density measurement and plasma current distribution diagnosis. Therefore, it is essential to research the surface morphology changing of the retroreflector systematically. Laser speckle interferometry technique is considered as a most promising method for real-time monitoring the PFMs surface morphology changing at plasma discharge intervals in the near future and its measurement accuracy and reliability have been adequately verified in the laboratory. One retroreflector served in 2019–2020 EAST Campaign is selected as a representative, compared with a brand-new retroreflector, to demonstrate that microscale surface morphology changing occurred on the internal reflection planes after bearing a whole EAST campaign plasma interaction. Meanwhile, the surface morphology of each internal reflection plane appears severely different features. Further research and analysis of the surface morphology are more contributed to evaluating the damage states of the retroreflector and providing more suggestions for the improvement and protection of the retroreflector. The surface morphology reconstruction results are given through a 3D visual exhibition and laser speckle interferometry technique is proposing a new research perspective for PWI research.