Numerical Study On Physical Properties Of The Resistive Wall Mode In Tokamaks

Magnetic confinement fusion device is the main device to study the fusion energy, and one of the major parameters of the device is the beta (β=2μp/B2(the ratio of plasma pressure to the pressure of the cinfining magnetic field) which decides the efficiency of the fusion device. However, for high temperature and high pressure state, many instabilities will appear in plasmas, especially, the growth of macroscopical magnetohydrodynamic (MHD) instabilities will largely limit the beta value. While the external kink mode (XK) as a macroscopical magnetohydrodynamic instability is one of the major obstacles that limits high beta value. It is the most dangerous ideal MHD instability mode, even can cause the discharge off. Because of the external conducting wall of the tokamak, a new grow-slowly unstable mode appears near the wall, that is the resistive wall mode (RWM). Even though the growth rate of the RWM is smaller than that of the XK, but during the scale of the plasma discharge, the development of the RWM can influence the normal operation of tokamak. So it is necessary to stabilize the RWM.Toroidal geometry system is adopt in this paper. The effect of the plasma with toroidal rotation on the resistive wall modes in tokamaks is studied numerically. First, a code for equilibrium quantities is adopted to calculate the Grad-Shrafranov equation. The equilibrium solution is the prerequisite for the code MARS to calculate the growth rate of the RWM. For this paper, the RWM is driven by current, the equilibrium current with Wesson’s equilibrium current profile is adopted to check the accuracy of the results. Then the plasma flow is considered to observe the instability of the RWM for changing plasma resistivity and plasma density distribution, as well as the diffusion time of magnetic field through the resistive wall and the ratio of the aspect of tokamak. Finally, a simply equilibrium current profile different from the previous profile is considered.The main structures of this paper are as follows. In chapter2, the effect of safety factor and plasma rotation on instability mode is studied. In the chapter3, the effect of plasma parameters on the resistive wall mode is investigated. In the chapter4, the plasma shear flow and equilibrium current is considered. Finally, a brief summary and discussion are given.It is found that the resistive wall mode can be suppressed by the toroidal rotation of the plasma. Through changing the parameters, it is found that the diffusion time of the conducting wall becomes to be infinite, as the conducting wall gradually turns into the ideal wall, the resistive wall is much easier to be stable. But there is little effect for plasma resistivity on the resistive wall mode, and when the edge plasma density is large, the growth rate of the resistive wall mode deceases. The aspect ratio of tokamak (the ratio of large toroidal radius of tokamak to the small radius of the plasma) becomes small, the device gets more close to the toroidal geometry, the growth rate is more small. The increase of equilibrium current gradient in the surface plasma can excite the growth of the instabiliy.