Three-dimensional Modelling Of Edge Lithium Transport And Its Impact On Divertor Heat Flux Deposition In EAST

Plasma-wall interaction is one of most important factors for steady-state operation in future magnetic confinement fusion devices.At the high power and long pluse diacharge condition,strong heat flux and particle flux from upstream plasma would transport along open magnetic field lines onto downstream divertot target,which induces eroding,melting and evaporating divertor target,and also shortening the used lifetime of divertor targets.Moreover,substantial of eroded impurities during penetration into the core plasma would dilute background plasma and increase the energy loss by impurity emission,which cools down background plasma,even terminates plasma discharge and fusion reaction.It is important for high performance and long pulse plasma discharge operation that using the advanced wall treatment technology not only improves surface properties of plasma-facing components(PFCs)materials and heat handling capacity,but also decreases the edge recycling.Lithium(Li)is considered as one of most promising wall treatment materials in future fusion devices.It is found that Li materials used in tokamak discharge experiment could mitigate interaction between the plasma and PFCs material,reduce eroded degree on divertor target and improve the plasma confinement ability.However,the Li transport and emission behaviors in threedimensional(3D)Scrape-off layer(SOL)of tokamak are still an open issue.Studies of edge impurity transport properties in tokamak devices are important to obtain a better understanding of impurity screening effects,radiation divertor plasma and plasma-wall interaction.Therefore,based on Li experimental discharge campaign of EAST device,3D edge fluid transport code EMC3-EIRENE has been applied to study Li impurity transport in the SOL plasma and heat flux deposition on divertor.In chapter 1,the limiter and divertor configuration of tokamak device and confinement mode in tokamak plasma are briefly reviewed.The description of Li materials application and actual simulation chievement of Li transport in tokamak is investigated.The chapter 2 introduces edge fluid transport model in magnetic confinement fusion device,derivation and simplification of basic physics equations.The 3D Monte Carlo code EMC3-EIRENE,construction of 3D computational mesh on EAST configuration and establishment of 3D boundary conditions are also addressed.The chapter 3 work is dependent on the liquid Li limiter(LLL)discharge experiment of EAST device,the 3D edge fluid transport code EMC3-EIRENE has been used to study edge plasma and impurity transport behaviors.The 3D spatial structure of the charge state and excitation radiation patterns of Li impurity can be understood by using field line tracing,which shows that the Li ions with different charge states exhibit different parallel transport behaviors in EAST edge plasma.The Li1+ and Li2+ ions transport along the toroidal direction shows s asymmetry distribution,while the Li3+ ions transport along the toroidal direction shows a symmetry distribution.Moreover,the 3D line-integrated LiII emission pattern simulated by EMC3-EIRENE code shows a reasonable qualitative agreement with the experiment results measured by the CCD camera system on EAST.An unresolved issue in the LLL experiment is that the species emitting the strong visible spectrum observed around the edge plasma region cannot be distinguished by the current experimental diagnostics on EAST.The detailed physical mechanism behind this problem is still unclear.The quantitative comparison of lithium,deuterium and carbon emissions indicates that the simulated deuterium emission pattern shows the same qualitative behavior as the experimental observation at the lower divertor region.The strong radiation experimentally observed at the upper divertor region is perhaps due to the mixing of the Li and deuterium emissions.The chapter 4 work is according to the Li powder injection(LPI)experiment on EAST device of low parameters plasma discharge,the EMC3-EIRENE code has been applied to investigate Li transport and divertor heat flux in LPI experiment.The qualitative comparison study shows a reasonable agreement between the EMC3-EIRENE simulated results and the experimental measurement.The Li1+ ions mainly populate at the upper private region,while the Li2+and Li3+ ions distribute at the upper X-point and upstream SOL regions.The synthetic 3D line-integrated LiII and deuterium emission distribution pattern obtained by EMC3EIRENE shows a similar structure with the experimental observation by the CCD camera system on EAST.The impact of the LPI poloidal locations has been studied to evaluate the variation of the Li impurity and background plasma transport behaviors.For the lower single null magnetic configuration of EAST,Li ions can be effectively screened for the downstream divertor injection due to the dominant friction force.However,Li injection at the outside midplane can enhance the Li impurity emission intensity,which is the most effective location to radiate more power.Resultantly,the reduced peak value of parallel heat and particle flux deposition on the divertor targets is found.The chapter 5 work is based on the LPI on EAST device of high parameters plasma discharge,the EMC3-EIRENE code has been conducted to study the edge plasma and Li transport properties in SOL plasma of EAST.The Li1+ and Li2+ ions density shows a toroidally non-axisymmetric distribution in different LPI position scenarios.With Li injection from upper private region,the Li3+ ions density shows a toroidally non-axisymmetric distribution.While the Li3+ ions density shows an axisymmetric distribution with Li injection from upper outer divertor region.Li injection from upper private region would shield Li ions with low charge state and restrain Li ions into core region.Li injection from upper outer divertor region would decrease peak value of perpendicular heat flux on divertor targets and its peak value is lower than 10 MW/m2.The radial penetration of Li3+ ions is lager than Li1+ and Li2+ ions.The improved Li injection flux from upper outer divertor region leads to enhanced profile of Li ions density at outside midplane and total Li ions amount,which increases the effective charge states in edge plasma.Furethermore,improved Li injection flux results in enhanced radiation power of Li impurity and decreased peak value of perpendicular heat flux on upper divertor plates.The conclusions and innovation points are summarized in chapter 6.Besides,the prospects of future work are discussed.