Simulation Study On The Impact Of Edge Three-dimensional Topology On Heavy Impurity On Transport In The EAST Tokamak

The impurity transport in tokamaks is an important issue.Resonant magnetic perturbation(RMP)is an important method for effectively controlling impurity transport,and its effectiveness in impurity control has been extensively observed in EAST,especially during magnetic field penetration.Experiments with RMP phase difference scans have revealed a clear dependence of impurity concentration on RMP phase difference.At lower toroidal mode numbers,RMP control of impurity transport is more effective,and the effect of RMP on impurity transport improves with increasing impurity mass.Although many experimental phenomena have been observed,the physical mechanisms of RMP’s impact on impurity transport are still unclear.In this paper,based on EAST experiments,using the Magnetohydrodynamic Resistive Spectrum(MARS-F)code to calculate the perturbation field,the impact of the edge three-dimensional topology in the EAST tokamak on impurity transport is studied through simulations from two aspects:the neoclassical toroidal viscosity(NTV)effect and the transport induced by stochastic magnetic fields.The impacts of impurity ion charge state,impurity mass,plasma response,RMP spectrum,toroidal mode number on NTV effect and stochastic magnetic field-induced transport are discussed.The first part of this work investigates the impact of the NTV effect caused by RMP on tungsten transport using the NTVTOK code,with a focus on the region of 0.8<ρ<0.9.The study found that the NTV effect on W1+is much greater than that on W20+,with the equivalent transport coefficient of W20+only on the order of 10-4～10-3m2/s,while the equivalent transport coefficient of W1+can reach 0.1～1 m2/s,which is close to the new classical diffusion coefficient of W1+.The numerical simulation results show that the flux of W1+exhibits a clear phase dependence on the RMP spectrum,and the W1+ flux obtained from NTVTOK is higher at low toroidal mode numbers compared to high toroidal mode numbers,which is qualitatively consistent with EAST experiments.The second part of this work simulated the impact of RMP-induced stochastic magnetic field on tungsten transport,focusing mainly on the region of 0.9<p<1.The research revealed that the impact of stochastic magnetic field on W20+is significantly greater than the impact on W1+.This paper compared the effective transport coefficients of W20+ taking vacuum assumption and considering plasma response,and found that the effective transport coefficient of W20+ is higher when the vacuum assumption is adopted.However,even when the plasma response effect is taken into account,the equivalent transport coefficient of W20+ in the stochastic magnetic field can reach 2～5 m2/s,which is 2～3 times that of the two-dimensional neoclassical diffusion coefficient of W20+.However,when the plasma screening effect is strong,the stochastic layer becomes narrower,and the impact of the stochastic magnetic field on the transport of impurity ions weakens,neoclassical transport may become the main factor affecting the transport of impurity ions.The dependence of the equivalent transport coefficient of W20+in the stochastic magnetic field on the RMP spectrum is in good agreement with EAST experiments when considering the plasma response effect,while the results under the vacuum assumption have a phase shift of about 60°compared to experiments.In addition,the impact of the stochastic magnetic field on W20+ is more significant at low toroidal mode numbers than that at high toroidal mode numbers,which is qualitatively consistent with the results of EAST experiments.In conclusion,the influence of NTV effect on low-charge state impurity ions is more significant compared to high-charge state impurity ions.However,the stochastic magnetic field has a greater impact on high-charge state impurity ions.When the plasma screening effect is weak,the stochastic magnetic field dominates the transport of impurity ions.But when the plasma screening effect is strong,the width of edge stochastic layer becomes narrower and its impact on impurity ion transport weakens,neoclassical transport may become the main factor affecting impurity ion transport.