| During tokamak devices operation, plasma-facing material (PFM) will be exposed to steady/transient heat flux and particle flow which come from the core plasma of tokamak. Meanwhile, the processes of plasma wall interaction (PWI) can result in a series of issues, such as, fuel retention, impurities formation, blistering, co-deposition and so on. How to solve the PWI issues is a key factor to decide whether the ITER project will be successful or not. The linear plasma generator can produce steady/transient plasma beam with similar parameters as edge plasma of tokamak. This kind of plasma beam can be used to irradiate the PFM to simulate the PWI processes. However, the realization of in-situ diagnosis of PFMs is very difficult and challenging due to the lack of suitable diagnostic technique. In this framework, the development of in-situ diagnosis technique of PFM for linear plasma generator and tokamak devices is a key issue which needs to be solved. The real-time and in-situ measurement of elemental compositions for PFM is very important for understanding the PWI processes, revealing the PWI mechanism and proposing the PFM optimum proposal.To solve these problems, this thesis developed an in-situ laser-induced breakdown spectroscopy (LIBS) technique for PFM diagnosis. The in-situ LIBS technique was applied to diagnose the elemental compositions of PFM in Magnum-PSI, DUT-PSI linear plasma generator and EAST tokamak. The key scientific issues about PWI, such as fuel retention, impurity formation, lithium (Li) co-deposition and so on, were studied in this thesis. The content of this thesis is organized as follows:In chapter 2, an in-situ LIBS diagnosis system for PFM was developed in the Magnum-PSI device. The LIBS system could obtain the signals of PFM elements with high temporal-spatial resolution under low background pressure of 10-1 mbar. This was the first time that the in-situ LIBS technique was used in the large linear plasma generator device. By using the high flux deuterium (D) plasma (1024 m-2s-1) and in-situ LIBS technique in Magnum-PSI, the characters of D retention and elemental distribution on pure tungsten (W), lithiated W, original graphite tiles and lithiated graphite tiles under different plasma fluences were studied. The results show that lithiation could suppress blistering on W surface. After 1.910 25m-2 fluence of D plasma exposure, the D signal in lithiated W was much higher than it in pure W. This is due to the intense chemical reaction between Li and D. With increasing the D plasma fluence to 6.2 10 25 m 2, the D retention was saturated in both pure W and lithiated W. The LIBS depth analysis show that the signals of Li, D and H decreased with depth, while W signal increases first and then keeps stable with depth. The balance between Li re-deposition and Li sputtering processes could be found during D plasma exposure. The off-line X-ray photoelectron spectroscopy (XPS) analysis show consistent results with LIBS about the elemental distribution. The XPS analysis in the LIBS laser ablation hole on lithiated Ws showed that the Li re-deposition was happens during the D plasma exposure.In chapter 3, the DUT-PSI linear plasma device based on the low pressure DC cascaded arc plasma source was set up. The plasma parameters of shock wave plasma beam which produced by DUT-PSI were diagnosed by a 2D optical emission spectroscopy system. The electron, vibrational and rotational temperatures of Ar/N2 shock wave plasma beam were measured. The results show that the plasma emission intensity, vibrational and rotational temperatures are high, while the electron temperature is low in compression zone of shock wave plasma beam. The electron, vibrational and rotational temperatures show significant difference, which is due to the nonequilibrium state in the low pressure shock wave plasma beam. After upgrading the electrode structure of DUT-PSI, plasma beam with similar plasma parameters as the divertor region was obtained for low temperature and high density. The electron temperature was 1-1.2 eV, and the electron density could reach 210 14 cm-3. This plasma beam could be used to simulate the PWI processes, such as fuel retention and lithiation. With the LIBS elemental chemical imaging system, the 3D distribution of elements in lithiated W was studied. The Li, H, O and Ar distribution had similar trend, while W distribution was different from others on the surface of lithiated W. The off-line XPS analysis proved the results of LIBS elemental chemical imaging. The chemical states on the laser ablation zone and lithiated W surface was also measured.In chapter 4, the EAST divertor graphite tile was off-line analyzed by LIBS, which was used in the EAST 2012 experiment for 5621 shots and more than 50000 s discharging. The depth profile behaviors of Li and D indicated that the D retention in divertor tile came from Li-D co-deposition processes during D discharge in EAST. The D concentration ratio (D/(D+H)) was estimated as 0.17 in Li-D co-deposition layer. This value was obtained below the surface layer of the divertor tile and could represent the D concentration ratio on the surface of divertor tile during EAST D discharge. A LIBS system has been developed to investigate the spatial distribution of PFMs elements under low pressure. The spatial profiles of LIBS signals of C, Si, Mo and continuous background were measured. The results show that the C, Si and Mo peak intensities increase first and then decrease from the center to the edge of plasma plume. This is due to the complicated interaction of bremsstrahlung, recombination and plasma dynamic expansion in the plasma. Moreover, the influences of laser spot size and laser energy density on LIBS signals of C, Si, Mo and H were also investigated. The other part of this chapter was the design of in-situ LIBS system for diagnosis of PFM in EAST tokamak. This is the first time that in-situ LIBS used on the superconducting tokamak with divertor design. The optical system was special designed, and the LIBS could diagnose more than 12 12 cm 2 area on the first wall at the high magnetic field side. In 2014 ESAT campaign, the in-situ LIBS was used to measure the elemental variation of PFM. The signals of Li, Mo, D, H, W, La, Ta, Si, Na and so on were obtained. The thickness of Li deposition layer increased from 4.0 μm to 9.0 μm after two times 45 g Li wall conditioning by evaporator, Li pellet injection and 194 shots discharging. The D retention ratio (D/(H+D)) was about 61%-64% on the Mo first wall in EAST. |
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