Global impurity detection of HL-3 tokamak using in situ fibered laser-induced breakdown spectroscopy

摘要: Investigating global impurity deposition on the plasma-facing components (PFCs) of fusion devices is crucial for their high-performance operation. In this study, an in situ fibered laser-induced breakdown spectroscopy (IF-LIBS) system with a large-scale scanning capability was developed and employed for in situ diagnosis of the surface impurities on PFCs in the HL-3 tokamak nuclear fusion device. The PFCs in HL-3 were scanned using IF-LIBS with a spatial resolution of approximately 30 mm on the first wall of the high-field side, 40 mm on the divertor and 50 mm on the first wall of the low-field side, depending on the PFC sizes. The substrate element (C) and impurity elements (Fe and Cr) on the PFCs were clearly observed from the in situ detection results of IF-LIBS. Because HL-3 is an all-carbon tokamak, Fe and Cr could be used to study the impurity deposition pattern of HL-3. The thickness of the impurity deposition layer was determined using applied ablation laser pulses combined with the ablation rates of the  eposited layer and graphite substrate obtained using a three-dimensional profiler. The absolute global impurity deposition pattern on the measured PFCs was obtained with the aid of depth profiling using the observed impurity lines (Fe and Cr) emission owing to LIBS with the number of applied laser pulses at one measurement location. The chemical imaging results of the impurity elements indicated that the impurity deposition distribution exhibited a onuniform impurity deposition pattern in the poloidal direction of HL-3. The peak deposition area was located in the divertor dome region, with a peak deposition thickness of up to 3 µm. Regions with minimal impurity deposition were observed in the midplane area on the high-field side, with a deposition thickness of approximately 1 µm. Moreover, the impurity deposition at the low-field side was slightly higher than that at the high-field side. The impurity pattern on PFCs correlates with the magnetic field configuration of HL-3 discharge and plasma particle flow, which was measured using an in situ visible camera and Langmuir probes.