Experimental Study On The Behavior Of Low-Z Impurity Ions In EAST Tokamak Plasmas

The lower divertor of the tungsten material of the EAST device is about to be put into use.With the further increase of the heating power,the interaction between the plasma and the plasma facing material will be stronger,resulting in a substantial increase in the impurity content.The presence of impurities dilutes the concentration of main particles,reduces the confinement performance of the plasma,and affects high-parameter steady-state operation.However,the low-Z impurities distributed in the plasma boundary region can reduce the plasma temperature through radiation,reduce the interaction between the plasma and the material,and reduce the sputtering of high-Z materials,thereby reducing the content of high-Z impurities entering the plasma.Therefore,real-time monitoring of low-Z impurities and transport research are very important to control the impact of impurity radiation during plasma discharge.With the increase of plasma temperature,most impurity ions have abundant radiation spectrum in the extreme ultraviolet(EUV)wavelength range.The study of extreme ultraviolet spectroscopy can not only provide information on the types and time evolution of impurities in the plasma,but also contribute to the study in impurity transport and atomic processes in fusion plasma.The main content of this thesis includes three parts.Firstly,in-situ absolute intensity calibration and in-situ wavelength calibration were carried out for the three newly-built fast extreme ultraviolet spectrometer diagnostic systems on EAST.Then,using the accurate in-situ wavelength calibration results,the characteristic spectrum of the low-medium Z impurity in the EAST plasma in the EUV wavelength range(10-500 A)was systematically identified.Finally,a preliminary study of impurity behavior was carried out using the identified characteristic spectral lines.In this thesis,the EAST Tokamak device helium plasma discharge density limit experiment is used to obtain continuous bremsstrahlung observations with high signal-to-noise ratio in the EUV wavelength range.The intensity of continuous bremsstrahlung in the EUV wavelength range is theoretically calculated by using the effective charge number(Zeff)of visible bremsstrahlung measured under these conditions.By comparing the experimental measured values and theoretical calculated values of the continuous bremsstrahlung radiation in the EUV wavelength range,the calibration coefficient curve of the fast extreme ultraviolet spectrometer system is obtained,and the in-situ absolute intensity calibration of the spectrometer system is realized.The fast in-situ wavelength calibration of the fast extreme ultraviolet spectrometer system is carried out by combining the single spectral line measurement with the line dispersion rate of the spectrometer system.At the same time,accurate in-situ wavelength calibration of the fast extreme ultraviolet spectrometer system is carried out by using multiple spectral line observations covering the whole waveband combined with the polynomial fitting method.The wavelength uncertainty introduced by different calibration methods is clarified,which improve the accuracy of spectral line recognition.In addition,the spectral resolution of the new boundary fast extreme ultraviolet spectrometer in FI and F VB data acquisition modes is analyzed by using the wavelength calibration results,and the installation position of the detector(CCD)is optimized according to the analysis results,which is expected to have better spectral resolution performance in the next round of experiments.The EUV spectra in the wavelength range of 10-500 A from low to medium Z impurity particles such as helium(He),lithium(Li),boron(B),carbon(C),oxygen(O),neon(Ne),silicon(Si)and argon(Ar)have been observed under different EAST discharge conditions using the rapid extreme ultraviolet spectroscopy(EUV)diagnostic system.The spectra are systematically analyzed based on the National Institute of Standards and Technology(NIST)database.A total of 227 spectral lines of 39 ionized states of impurity elements,such as He+(He Ⅱ)、Li+-Li2+(Li Ⅱ-Ⅲ)、B3+-B4+(B Ⅳ-Ⅴ)、C2+-C5+(C Ⅲ-Ⅵ)、O2+-O7+(O Ⅲ-Ⅷ)、Ne+-Ne9+(Ne Ⅱ-Ⅹ)、Si4+-Si11+(Si Ⅴ-Ⅻ)Ar9+-Ar15+(Ar Ⅹ-ⅩⅥ)are successfully identified.And a database of ionization energy,spectral line wavelength and transition of impurity ions was established.This database can be used as an important reference for impurity diagnosis and impurity research in high temperature plasma of magnetic confinement fusion.Finally,the impurity behavior is studied based on the results of in-situ absolute intensity calibration and spectral line identification.Including the quantitative study on the evolution of impurity ion flux with discharge time,the comparative study on the continuous effect of lithiation and silicide wall treatment,and the analysis of the characteristic confinement time of impurity particles in the neon and argon injection experiments.Through the above work,we have achieved reliable absolute intensity measurement of passive spectroscopy in the extreme ultraviolet wavelength range,which makes the quantitative study of impurity behavior possible.The accurate wavelength calibration of passive spectrum in the EUV wavelength range is realized,greatly improving the accuracy of spectrum wavelength measurement,which lays the foundation for future high-Z impurity spectral line observation and identification and transportation research.A EUV lines database of low-medium Z impurity has been established,which can be used as an important reference for future magnetic confinement fusion high temperature plasma impurity diagnosis and impurity research.