The morphology monitoring of the wall surface of the Tokamak is of significance for understanding the erosion and deposition phenomena that occur on the wall surface. Laser speckle interferometry (LSI) is a technique that can measure the three-dimensional morphology of surfaces on-line in-situ, which can achieve real-time non-destructive measurement. In this paper, the influence of continuous white light emitted by plasma discharge on the LSI measurement is investigated off-line. The experimental results show that the existence of white light background is not conducive to the measurement of three-dimensional morphology of the plasma-facing-components (PFCs) by LSI in Tokamak. Therefore, we propose an improved laser speckle interference (ILSI) technology based on frequency domain and spatial domain filters to depress white light background. The experimental results show that the ILSI works well. This lays a theoretical foundation for the future application of LSI technology to Tokamak devices.
Temporal phase-shifting interferometry technique (TPSI) has high accuracy in surface topography metrology and has been designing to diagnose the surface variation of plasma-facing materials (PFMs) in Tokamak. But the mechanical vibration of the Tokamak device will lead to the decrease of the measurement accuracy or even incorrect result. In order to solve the problem more, it is much desired to study the influence of the vibration on the topographic measurement in the broad parameter scope. Series experiments in the different vibration frequencies, amplitudes, modes and different deformation amounts and detection wavelengths were carried out in this work.
Aiming at building the real-time measuring system of surface morphology of Plasma-Facing Components (PFCs) in fusion devices, an optical approach based on Laser Speckle Interferometry (LSI) is in development in our laboratory. To preserve high temporal resolution, the temporal phase shifting approach was introduced. However, this approach is sensitive to vibrations, which decreases the accuracy of morphology measurement. Considering the periodic vibration of the tokamak device itself, it is important to study the influence of the periodic vibration on online surface morphology measurement of PFCs. In this paper, we specify the effects of amplitude and frequency of periodic vibration on surface morphology measurements based on LSI measurement system. Benchmark tests are performed on the Molybdenum (Mo) material, which is commonly used as PFCs in Experimental Advanced Superconducting Tokamak (EAST).
Monitoring the deformation caused by wall erosion and deposition on the Plasma-Facing Components (PFCs) in tokamak has been essential issues for the maintenance of a long duration plasma discharge and safety. As an in situ, real-time and non-destructive optical diagnostic technique, Laser Speckle Interferometry (LSI) based on temporal phase-shifting approach has been considered as the most potential approach for the measurement of erosion and deposition on PFCs. This paper focuses on the measurement of the deposition morphology and thickness based on the temporal phase-shifting laser speckle interferometry. Here the deposition was conducted by Pulse Laser Deposition (PLD) in a vacuum chamber, which is simulated to the deposition process on PFCs. The LSI measurements are compared with those of profilometry and the results show that the temporal phase-shifting laser speckle interferometry is capable of online measuring deposition morphology as well as thickness. The LSI approach has great possibility for the further application on the real-time monitoring impurity and fuel deposition on PFCs in fusion devices.
A dual-wavelength phase-shifting speckle interferometry approach has been proposed to diagnose the topography of plasma-facing materials (PFMs) in tokamak. The conventional speckle interferometric surface measurement, which uses single-wavelength, can offer excellent vertical resolution, but limitation in measuring large height step and phase ambiguity would occur during their application. To solve the problem, a dual-wavelength method was developed. Experiments were conducted on molybdenum (Mo) sample, which is related to PFMs of experimental advanced superconducting tokamak (EAST), and a laser ablation method was adopted to simulate the erosion happed on PFMs. The laser ablation craters were measured by both single-wavelength and dual-wavelength phase-shifting speckle interferometry, and a multistep phase-shifting method has been investigated for their effectiveness on reducing noise in calculating the phase map. This work demonstrates the superiority of the dual-wavelength speckle interferometry and the feasibility of applying the measurement system in topographic measurement of PFMs in EAST.
Digital speckle pattern interferometry (DSPI) can diagnose the topography evolution in real-time, continuous and non-destructive, and has been considered as a most promising technique for Plasma-Facing Components (PFCs) topography diagnostic under the complicated environment of tokamak. It is important for the study of digital speckle pattern interferometry to enhance speckle patterns and obtain the real topography of the ablated crater. In this paper, two kinds of numerical model based on flood-fill algorithm has been developed to obtain the real profile by unwrapping from the wrapped phase in speckle interference pattern, which can be calculated through four intensity images by means of 4-step phase-shifting technique. During the process of phase unwrapping by means of flood-fill algorithm, since the existence of noise pollution, and other inevitable factors will lead to poor quality of the reconstruction results, this will have an impact on the authenticity of the restored topography. The calculation of the quality parameters was introduced to obtain the quality-map from the wrapped phase map, this work presents two different methods to calculate the quality parameters. Then quality parameters are used to guide the path of flood-fill algorithm, and the pixels with good quality parameters are given priority calculation, so that the quality of speckle interference pattern reconstruction results are improved. According to the comparison between the flood-fill algorithm which is suitable for speckle pattern interferometry and the quality-guided flood-fill algorithm (with two different calculation approaches), the errors which caused by noise pollution and the discontinuous of the strips were successfully reduced.
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