Simulation Study Of Tungsten Impurity Sputtering And Transport On EAST

The divertor,as the key particle and energy deposition region in magnetic confinement tokamak devices,bears high heat load transported from the core plasma.Tungsten is selected as the divertor target material for EAST tokamak and International Thermonuclear Experimental Reactor(ITER)due to its favorable physical and chemical properties,and is also the preferred material for the first wall and divertor target of the future Chinese Fusion Engineering Test Reactor(CFETR).The corrosion and sputtering of tungsten divertor target material and significant power loss induced by the accumulation of W impurity in the core plasma,will directly affect the lifetime of tungsten divertor components and confinement performance of core plasma.Controlling the corrosion and sputtering on the tungsten divertor target strictly is one of the key issues that must be solved by EAST and future fusion reactors.Therefore,it is of great importance to study the sputtering and transport of tungsten impurities for future long-pulse high-confinement discharges and enhancement of the compatibility between the core and boundary in future fusion reactors.The thesis conducts the simulation study of tungsten impurity sputtering and transport on EAST tungsten divertor by using the large-scale boundary simulation code SOLPS-ITER.The major research contents are as follows:(1)The effects of several different bundled schemes on the distribution of divertor plasma parameters and tungsten impurity behaviors are investigated for an L-mode discharge of EAST for the first time.Compared with full tungsten treatment,it is found that bundled charge state model can significantly speed up the simulation process and conserve computing resources.In the low recycling regime,the differences of plasma parameters at both divertor targets are within 15%between different bundling schemes and full W treatment.The errors of tungsten concentration and the effective ion charge number for bundled models are within 40%inside the separatrix.In the high recycling regime,there is no significant difference about divertor plasma parameters between bundled models and full W charge state model,which can be attributed to decreased temperature and W source in the divertor region.Furthermore,the selection of bundling scheme will affect the evaluation of radiation power loss,especially for radiation power loss inside the separatrix.It is important to avoid bundling the intermediate charge states W+16-W+30 with the highest charge state W+74 together.(2)The effects of bundling scheme on plasma parameters and W impurity behaviors are performed for an H-mode discharge with external impurity seeding.It is shown that the highly resolved bundled model "jett" has little influence on the ionization balance and transport of neon(Ne)impurity,and has little difference on radiation power loss and tungsten source produced by Ne species.It indicates that bundled model "jett" can describe divertor plasma parameters and tungsten impurity behaviors well by comparative analysis with full W treatment.In addition,the differences of transport intensities have a significant influence on divertor target parameters,tungsten impurity sputtering and erosion rate by using bundled model "jett".(3)The effects of different magnetic configurations(horizontal target configuration and vertical target configuration)on plasma parameters at targets、neutral density、tungsten impurity sputtering and transport behavior,are investigated detailedly.In low recycling regime,there is a noticeable tungsten impurity ionization source above the stagnation point of poloidal velocity in vertical target discharge,which makes it easier for the tungsten impurity at the outer target to escape from the divertor and transport upstream after being ionized.The electron temperature in the far SOL region of vertical target discharge is obviously higher than that of horizontal target discharge,resulting in higher tungsten sputtering in the far SOL region.In high recycling regime,the relative location between the stagnation point of tungsten impurity poloidal velocity and ionization source is relatively far,which enhances the divertor screening on tungsten impurities.(4)The influence of helium(He)plasma discharge on tungsten impurity sputtering and transport is studied in detail,and compared with deuterium(D)plasma discharge.It is shown that the tungsten eroded flux of He plasma discharge is higher than that of D plasma discharge with the same upstream electron density due to higher ion temperature.Moreover,higher gradient of ion temperature also makes the thermal force and net force of tungsten impurity much greater than that of D plasma discharge,which tends to transport tungsten impurity upstream.There is also obvious ionization source of tungsten impurity near the stagnation point of He+1 poloidal velocity,He+1 will drag tungsten impurity ions upstream.Therefore,upstream concentration of tungsten impurity and effective charge number is higher in He plasma discharge.In addition,the effects of He and D discharges on tungsten sputtering and radiation with different electron densities are analyzed.