Experimental Study On Tungsten Impurity Transport With Auxiliary RF Heating In EAST Plasma

In tokamak,the plasma-wall interaction can produce the impurity particles which have significant impact on plasma performance.Tungsten is a unique candidate material for plasma facing component in magnetic fusion devices with high sputtering threshold,high melting point and low hydrogen retention rate.However,tungsten as high-Z materials cannot be completely ionized even in high-temperature plasma.The accumulation of tungsten ions in plasma core can enhance radiation power loss and degrade plasma performance,even lead to the plasma disruption.Tungsten accumulation is a key issue to be solved in realizing steady-state H-mode high power long pulse operation.Therefore,it is important to understand the behavior of tungsten and control its accumulation in plasma.There are various auxiliary heating systems in EAST device.It is experimentally found that radio frequency heating can effectively suppress tungsten accumulation,which increase the possibility to realize long pulse high performance plasma operation in EAST.Impurity diagnosis is fundamental for studying of impurity transport.The studies related to impurity transport in this thesis are based on the extreme ultraviolet(EUV)spectrometer system.The upgrade and development of system is one of main works in this thesis.First,the performance of two newly developed fast time space-resolved EUV spectrometer working at short wavelength range are tested.This system is equipped with 2400 g/mm grating and CMOS detector,which greatly improve the spectral and temporal resolution respectively,make it capable of observing rapid change in the radial profile of impurity line emission.Secondly,the observation range of spaceresolved EUV spectrometer system working at long wavelength range was expand to enable measurement of the full vertical profile of impurity line emissions in plasma.Thirdly,in order to completely study behavior of impurities in plasma the fast-timeresponse EUV spectrometer systems were upgrade to monitor the impurity ions in low ionization at plasma edge.In terms of data processing,an interactive interface is developed based on the MATLAB software for the space-resolved EUV spectrometer.The functions of the newly developed software include data reading,wavelength calibration,viewing chord alignment,time synchronization,emission line intensity calculation and profile plotting.The development and application of this newly developed software largely improve the efficiency of data analysis and guarantee the real-time data analysis.The calculation method of impurity ions density profile is developed based on the vertical intensity profiles observed by space-resolved EUV spectrometer.The behavior of high-Z metal impurities in L-mode and H-mode plasmas with and without ion cyclotron resonance heating(ICRH)is quantitatively studied.It is found that the impurity ion density considerably increases in the H-mode plasma compared with the L-mode plasma.The radial location of impurity ions moves outwardly in the H-mode plasma,reflecting the high central electron temperature.When the 0.7 MW ICRH heating is additionally supplied,the metal impurity ions density increased by 50%in the H-mode discharge,and the radial location of impurity ions moves inwardly.And with the increase of ICRH power,the metal impurity content in the plasma core further increases.Based on the newly developed EUV spectrometer systems and data processing methods,the following tungsten impurity transport studies were carried out in this thesis.The effect of low hybrid wave(LHW)heating on tungsten transport in neutral beam injection(NBI)dominant H-mode plasma is study on EAST.It is observed experimentally that the electron temperature and the fELM increase,the toroidal rotation velocity and the content of tungsten in plasma core decreases significantly after LHW injection in plasma with low q95.And the electron-scale microturbulence amplitude increase slightly during LHW phase which means that the turbulent impurity transport is enhanced.Similar results were observed in the plasma with high q95 where the tungsten profiles are flattened and the content of tungsten in plasma core decreases nearly 100%during the LHW phase.The transport coefficient of tungsten impurity has been simulated by TGYRO.The simulated results suggest that the turbulent diffusion and neoclassical pinch dominant the tungsten transport.During LHW phase,the turbulent diffusion of tungsten is enhanced while the neoclassical convection is weakened.The simulated results also reveals that the toroidal rotation increases the neoclassical convection and leading to the inward pinch of tungsten.Therefore,LHW affects tungsten impurity transport in two ways:LHW heating causes an increase in the turbulent diffusion of tungsten by increasing the electron temperature,and decreases the plasma toroidal rotation velocity and reduces the inward neoclassical convection of tungsten.Subsequently,the impact of giant sawtooth oscillations on tungsten ion is study.It is found that the tungsten ions inside the inversion radius are affected by the sawtooth crash.The result from shows that the tungsten impurity accumulates in the narrow region of plasma core during sawtooth phase,and the gradient of tungsten profile inside inversion radius is much larger than that outside the inversion radius.The rapid change in W XXVII,W XXX and W XXXIII radial profile during a single sawtooth period are clearly observed with sufficient intensity by newly developed fast-time space-resolved EUV spectrometer systems.It is preliminarily inferred that the giant sawtooth has significantly impact on the radial transport of tungsten impurity ions in plasma core.The integrated EUV spectrometer diagnostic systems have been established,which makes the study of impurity transport more complete.The quantitative study of impurity behavior is realized by developing calculation method for impurity density profile.The mechanism of the impact of different heating on tungsten impurity transport has been studied,which can be used an important reference for the control of tungsten accumulation utilizing auxiliary heating in the future.