The diagnosis of the fuel retention and impurity deposition on the plasma facing components (PFCs) is very important for monitoring plasma-wall interactions and improving the performance of long-pulse operation for tokamak devices. In this study, a remote in situ laser-induced breakdown spectroscopic (RIS-LIBS) system has been developed to be an effective and routine method for the diagnosis of the composition of the PFCs on Experimental Advanced Superconducting Tokamak (EAST). The RIS-LIBS system can be operated between EAST discharges via a remote network control system. This allows a flexible diagnosis for the PFCs at a specific EAST discharge operation or under planned plasma scenarios according to the experimental requirement. Measurements on the fuel retention and impurity deposition of the PFCs have been performed for the test of the RIS-LIBS system, and the depth resolution and the lateral resolution of the RIS-LIBS system have been achieved to be ∼100 nm and ∼3.0 mm, respectively. For the test of detectable elements, the fuel (deuterium) and impurities have been detected and identified clearly. In addition, the measurement of fuel abundance on the first wall as a function of the days of EAST deuterium plasma discharges has been carried out for the first time. These results well manifest a significant prospect of the RIS-LIBS for the diagnosis of the PFCs in the upcoming fusion devices like China Fusion Engineering Test Reactor (CFETR) and ITER.

In this work, laser-induced breakdown spectroscopy (LIBS) approach was applied to Experimental Advanced Superconducting Tokamak (EAST) device for in situ diagnosing the lithium-wall conditioning processes and the Li-H/D co-deposition on the inner board of the first wall of EAST. The fuel of D and the co-deposition impurities, such as H, Li, Ca, Na and Mo were clearly observed on the surface of the first wall. During the processes of Li-wall conditioning, the Li signal intensity increases with the increase of the time of Li-wall conditioning, and the average deposited rate of Li was about 0.522 μm h -1 . The study of Li-coating layer indicates that LIBS technique can be used to assess the degree of re-deposition on the first wall. The variation of H/(H+D) as a function of the days of D-discharge demonstrates that Li-wall conditioning technique can significantly reduce the H/(H+D) ratio in the vacuum vessel due to the strong H/D adsorption capability of Li and enhance long-pulse H-mode plasma operation. The results indicate that LIBS technique can be used for in situ analysis of co-deposition and D retention on the first wall of EAST.

An experimental setup has been designed and realized in order to optimize the characteristics of laser-induced breakdown spectroscopy system working in various pressure environments. An approach combined the normalization methods with the partial least squares (PLS) method are developed for quantitative analysis of molybdenum (Mo) element in the multi-component alloy, which is the first wall material in the Experimental Advanced Superconducting Tokamak. In this study, the different spectral normalization methods (total spectral area normalization, background normalization, and reference line normalization) are investigated for reducing the uncertainty and improving the accuracy of spectral measurement. The results indicates that the approach of PLS based on inter-element interference is significantly better than the conventional PLS methods as well as the univariate linear methods in the various pressure for molybdenum element analysis.

Laser-induced breakdown spectroscopy has been recognized as a significant tool for element diagnostics in plasma-wall interaction. In this work, a one-dimensional numerical model is developed to simulate the laser ablation processes of a molybdenum (Mo) target in vacuum conditions. The thermal process of the interaction between the ns-pulse laser with wavelength of 1064 nm and the Mo target is described by the heat conduction equation. The plasma plume generation and expansion are described by Euler equations, in which the conservation of mass density, momentum and energy are included. Saha equations are used to describe the local thermal equilibrium of electrons, Mo atoms,

Impurity seeding is the major technology for divertor power exhaust. In this work, the impact of N and Ne impurity seeding on the behavior of neutrals in the divertor region was systematically studied based on the HL-2A tokamak. The results demonstrated a strong correlation between the target deuterium molecular density and the target electron temperature after N/Ne impurity seeding. In addition, it was found that deuterium atoms played a more important role in reducing the electron temperature of the target after the Ne impurity injection at Te <15 eV than that of N seeding. Moreover, the deuterium radiation atom excitation channel was stronger after the Ne impurity injection than the N impurity. It was also found that the N impurity radiation in the divertor can reach several times of the Ne impurity radiation under the high upstream density conditions. The core effective charge number Zeff was larger after the Ne impurity injection than N impurity injection, indicating that the Ne impurity was more likely to dilute the plasma.