Depth Profile Analysis Method In Plasma Face Materials Based On Laser-induced Breakdown

During the operation of Tokamak magnetic confinement fusion device,a strong interaction occurs tween plasma and plasma-facing wall materials(PFM).This process will cause physical sputtering,chemical corrosion and other damage to PFM,and there are problems such as fuel retention and impurity deposition.Therefore,real-time monitoring of PFM and impurity deposition detection is the most important thing to ensure the safe,stable and efficient operation of Tokamak magnetic confinement fusion device.Laser-induced breakdown spectroscopy(LIBS)is currently the preferred element analysis technique for insitu on-line detection of tokamak magnetic confinement fusion devices,and has been extensively studied in several tokamak magnetic confinement fusion devices wordwilde.LIBS is a qualitative and quantitative analysis technique based on atomic excitation.This technique has the advantage of depth element quantitative analysis of elements because it can generate high-temperature plasma by laser ablation and collect the characteristic spectum generated by high-temperature plasma to analyse sample.However,depth analysis based on LIBS cannot achieve quantitative analysis of depth values at present.Other depth measurement instruments,such as confocal microscope,are required as auxiliary equipment,which increases the complexity of equipment testing and limits the function of real-time insitu detection.In addition,the non-scaling quantitative analysis method for LIBS has low computational accuracy.Therefore,it is necessary to develop quantitative analysis of elements at different depths by LIBS and provide a method for quantitative analysis of elements at insitu,real-time and dynamic longitudinal depths.Moreover,tungsten material is one of the main materials for plasma wall materials,which has been selected as the first wall material and deflector material for many tokamak devices due to its advantages of high melting point and high physical sputtering resistance.Based on the above aspects,this paper mainly discusses the method of depth quantitative analysis of lithium and molybdenum in tungsten materials based on LIBS.The specific contents are as follows:In the first chapter,the technical research on the detection of impurity elements caused by the deposition of ion impurities in the tokamak magnetically constrained fusion device is investigated.Based on the fact that LIBS is the preferred technical means to solve this problem,the advantages and disadvantages of LIBS as well as the current limitations and key issues of LIBS are investigated.A method for quantitative analysis of elements at different depths by laser-induced breakdown spectroscopy is proposed.In the second chapter,the theoretical basis of LIBS is expounded,and the experimental platform and experimental instrument parameters are described.On this basis,the ablation depth of tungsten materials by LIBS is analyzed.The results show that there is a linear relationship between the number of laser pulses and the ablation crater depth,and the intensity of the main atomic lines of tungsten decreases with the increase of the ablation crater depth.The intensity analysis of plasma temperature and signal-to-back ratio shows that both plasma temperature and signal-to-back ratio increase with the increase of ablation crater depth.In the third chapter,the machine learning algorithm combined with LIBS is used to classify and identify the spectra corresponding to different laser pulses.The results show that the spectra corresponding to different laser pulses are different in data.On this basis,machine learning algorithm combined with LIBS is used to predict the depth of ablation crater by regression.The predicted depth of ablation crater by this method is consistent with that measured by confocal microscope,which proves the feasibility of machine learning algorithm combined with LIBS.In the fourth chapter,a new uncalibrated method for LIBS is explored,which is different from the most commonly used uncalibrated method at present,that is,the free calibration method.The new uncalibrated method is based on Maxwell’s velocity distribution law and Doppler effect.In this chapter,the principle of the new uncalibrated method is expounded in detail,and the element contents of various samples are calculated by the free calibration method and the new uncalibrated method,respectively.The results show that the quantitative analysis results of elements by this method are accurate.In the fifth chapter,machine learning algorithm combined with LIBS is used to predict the ablation crater depth of the test sample,and the molybdenum content in tungsten material is calculated by calibration method,and the lithium content in tungsten material is calculated by two non-calibration methods.Finally,the depth distribution of molybdenum and lithium in tungsten material is analyzed according to the prediction results of ablation crater depth.The analysis results show that this method can predict the depth distribution of elements,and the prediction results have reference value.In this paper,a method for in-situ,real-time and dynamic quantitative analysis of elements in longitudinal depth by LIBS is presented.The research content of this paper can provide a feasible method for quantitative analysis of depth elements by LIBS,and provide a technical reference for analysis of impurity deposition and fuel retention of plasma wall materials in magnetic confinement fusion device.At present,the shortcoming of this method is that the prediction accuracy of ablation crater depth based on machine learning algorithm combined with LIBS still needs to be improved,and more data are needed to explore the portability of the method.At the same time,the accuracy of element quantitative analysis needs to be improved.However,its application prospect is promising.The quantitative analysis method of depth elements based on LIBS proposed in this paper has wider applicability and can be extended to more research fields.