3-D Equilibrium Reconstruction Under Resonant Magnetic Perturbations On EAST

The Magnetohydrodynamics(MHD)equilibrium,namely the internal balance between the pressure of the plasma and the electromagnetic forces,is a basis of both theoretical considerations and physics interpretation of experimental results for magnetically confined fusion.With the toroidal symmetric configuration,the 2-dimentianal(2-D)EFIT code is most widely used for tokamak equilibrium reconstruction.Nevertheless,designed for Edge-Localized Modes(ELMs),the Resonant Magnetic Perturbations(RMP)will induced the 3-D magnetic topology and the tokamak equilibrium turns to be 3-D equation.Recently EAST has been equipped with RMP system,which requires a more accurate 3-D equilibrium reconstruction.This thesis focuses on the 3-D equilibrium reconstruction under RMP on EAST,including the fast 3-D magnetic topology modeling with linear code,and 3-D nonlinear resistive equilibrium reconstruction with HINT code.The RMP can produce the magnetic island on the resonant rational surface and the overlapping of islands may easily occur in the plasma edge region leading to stochastic magnetic topology.In order to understand the mechanism by which the RMP mitigates or suppresses the ELMs,the topological study of the edge magnetic field is a critical issue and we have developed a fast and light program in Fortran with vacuum approximation and local ideal plasma response approximation to model the magnetic topology on EAST.By solving the summation of 2-D equilibrium magnetic and RMP field in vacuum approximation,the thesis narrates the way of topology analysis in the flux coordinate and cylindrical coordinate in detail,which is helpful to understand the RMP 3-D effects on magnetic topology.On the other hand,the plasma response will induce the rational surface current to shield the RMP field.Using the current filament methods,the surface screening current is modeling to offset the resonant field component on the corresponding rational surface in the local ideal plasma response approximation,the thesis presents the magnetic topology when RMP is shielded.Furthermore,through comparing with footprint splitting phenomenon induced by RMP,the minimum p profiles on edge stochastic field lines agree well with the experimental particle flux observation in both two approximations.The difference is that the plasma response resizes the minimum p value around the flux peak point on the divertor target As charged particle diffusion along field lines is much larger than perpendicular,the model implies that the 3-D particle flux distribution to the divertor results from 3-D magnetic topology induced by RMP,the local ideal plasma response changes the field line penetration depth while remaining similar profile relative to vacuum approximation.The vacuum and local ideal plasma response approximation are the two limit cases when RMP superposed,namely completely penetration or shielding.In general,the real case should be in-between.Besides,the additional RMP field will upset the original 2-D equilibrium and the pressure distribution should be changed,which the two approximation could not deal with.Hence we use the nonlinear 3-D equilibrium HINT code to reconstruct the 3-D equilibrium under RMP on EAST.The HINT does not assume the existence of perfectly nested flux surface based on the relaxation method,which can give more precise pressure profile and magnetic distribution,especially in the pedestal region under RMP.As the 3-D equilibrium reconstruction given by HINT is a nonlinear resistive solution,it can provide references for the further study of nonlinear analysis between RMP and plasma response.And this work will make contributions to 3D plasma physics studies,which has the great significance to the combination of simulation and experiment on EAST.The last part of the thesis is the experimental analysis of plasma anisotropic degree induced by Lower Hybrid Wave(LHW)heating on EAST,and its dependence on the plasma density,LHW heating power and electron temperature.Particularly the anisotropic degree factor can reach σ～1.8 at low electron density with high LHW heating power.This quantitative evaluation for the plasma anisotropy may be helpful to more accurate 3-D equilibrium reconstruction on EAST with pressure tensor in the future.