In this paper, the influence of magnetic field strength on laser-induced breakdown spectroscopy (LIBS) has been investigated for various pressures. The plasma plume was produced by employing Q-switch Nd:YAG laser ablation of an Al-Li alloy operating at a 1064 nm wavelength. The results indicated that the LIBS intensity of the Al and Li emission lines is boosted with an increase of magnetic strength. Typically, the intensity of the Al I and Li I spectral emissions can be magnified by 1.5-3 times in a steady magnetic field of 1.1 T compared with the field-free case. Also, in this investigation we recorded time-resolved images of the laser-produced plume by employing a fast ICCD camera. The results show that the luminance of the plasma is enhanced and the time of persistence is increased significantly, and the plasma plume splits into two lobes in the presence of a magnetic field. The probable reason for the enhancement is the magnetic confinement effect which increases the number density of excited atoms and the population of species in a high energy state. In addition, the electron temperature and density are also augmented by the magnetic field compared to the field-free case.
During laser ablation, the spectral emission intensity, plasma temperature and electron density increased significantly with increasing sample temperature.
Laser-induced breakdown spectroscopy (LIBS) is a powerful analytical tool for realtime diagnostics and detection of multiple elements deposited at the first wall of magnetically confined plasma fusion devices. Recently, we have tested LIBS in our laboratory for application to in situ real-time diagnostics in the fusion device EAST. In this study, we applied polarizationresolved LIBS (PR-LIBS) to reduce the background continuum and enhance the resolution and sensitivity of LIBS. We used aluminium (Al) (as a substitute for Be) and the first wall materials tungsten (W) and molybdenum (Mo) to investigate polarized continuum emission and signal-tobackground ratio (SBR). A Nd:YAG laser with first, second and third harmonics was used to produce plasma. The effects of the laser polarization plane, environmental pressure and polarizer detection angle were investigated. The spectra obtained without using a polarizer (i.e. LIBS) were compared with those obtained with a polarizer (PR-LIBS). Distribution of emission spectral intensity was observed to follow Malus' law with respect to variation in the angle of detection of the polarizer. The spectra obtained by PR-LIBS had a higher SBR and greater stability than those obtained by LIBS, thereby enhancing the reliability of LIBS for quantitative analyses. A comparison of Al, Mo and W showed that W exhibited a higher continuum with stronger polarization than the low-Z elements.
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.
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