Research On Two-dimensional Numerical Simulation Of Optimized Current Profile Control

Current density profile distribution control is an important research topic to realize high constrained mode(H).In this paper,based on the experimental discharge parameters of J-TEXT Tokamak,the spatial distribution structure of magnetic field and flow field in the discharge process of the device is studied by using the 2D plasma equilibrium model,and the influence of different external driving current profiles on the plasma confinement performance is explored,the main research contents are as follows:(1)Plasma equilibrium equations based on two-dimensional current carrying type,the flow field effect is regarded as a first-order small quantity,and the structure distribution characteristics of magnetic field and self-consistent flow field are analyzed.The numerical simulation results show that: only the zero order equilibrium magnetic surface has no radial magnetic field and radial flow field,for the equilibrium magnetic surface of order one and above,even if it is converted to the traditional magnetic surface coordinates(zero order),there are still radial magnetic field and radial flow field.The 1,2,3,4 order magnetic field vector distribution maps on the magnetic surface coordinate show 2,4,6,8 pole field structures respectively,Spontaneous magnetic reconnection exists locally.At the same time,it is found that the self-consistent flow field has a multi-pole field structure similar to the magnetic field,and there are local eddy currents.(2)Based on the three-dimensional magnetic field structure distribution of Tokamak,the generalized safety factor has anisotropic structure characteristics,and there are obvious differences in the distribution on the high field side,the low field side and the middle vertical plane,The distribution of safety factor in the middle vertical plane is close to the structural characteristics of the traditional magnetic surface coordinate system.The generalized safety factor,which takes into account the higher-order toroidal and angular magnetic field,can greatly modify the distribution of safety factor in the traditional magnetic surface coordinates,especially in the plasma core.Therefore,the global distribution characteristics of safety factor profile must be used to evaluate the plasma discharge performance of Tokamak.(2)The influence of external driving current with different injection positions,amplitudes and broadening on the plasma equilibrium configuration is preliminarily studied,and the driving current distribution characteristics of forming weak reversed magnetic shear mode are explored.By increasing the width of driving current density,the safety factor in the core region can exceed 1.0,which is conducive to improving the plasma confinement performance.