Effect Of Current Profiles In Equilibrium On Non-Ideal MHD Modes In Tokamaks

The performance of fusion device is determined by the magnetic-confinement capacity on fusion plasma. It is found from research that since the presence of ideal magnetohydrodynamic (MHD) instability, the confinement capacity is limited and a beta limit exsits in magnetic-confinement fusion plasma. To raise the efficiency of fusion device and realize the net energy output, increasing the beta limit and suppressing the ideal MHD instability is very necessary. Equilibrium current is an essential requirement when theoretical studies on the MHD instability problem. How to choose a simple and feasible equilibrium current profile is what we care for. In this thesis, the effect of equilibrium current profile on MHD instability is studied numerically, and the results would have good theoretical guidance meaning on tokamak plasma MHD instability research.In this paper, the equilibrium current profiles are given, the equilibrium configurations are established under different equilibrium current profiles. By numerically solving the linearized MHD equations for ideal plasma and non-ideal plasma which has viscosity or resistance, we study the effect of equilibrium current on the ideal and non-ideal MHD instability, and the stabilizing effect of plasma viscosity and resistance are discussed as well.The research results show that, for static ideal plasmas in tokamaks, different parameters s (different equilibrium current profiles) have effect on ideal MHD instability. The larger parameter s is, the perturbation qualities increase more slowly, the system enters the linear growth phase later, and obtains smaller instability growth rate. That means when the curvature of equilibrium current profile is small, the system is more unstable. Furthermore, it's found that the lower poloidal mode is relatively more unstable.When taking into account of plasma viscosity or resistance, it is found that, the perturbation qualities and instability growth rates can be suppressed effectively by plasma viscosity or resistance, and the larger parameter with relatively smaller instability growth rate, so plasma viscosity and resistance have stabilizing effect. Moreover, for the non-ideal MHD system which has plasma viscosity or resistance, the lower poloidal mode is relatively more unstable as before.As for the non-ideal plasma which has viscosity or resistance, according to the research on the effect of the equilibrium current on non-ideal MHD instability, the results show that, the same as the ideal MHD plasma, the larger parameter s is, the perturbation qualities increase more slowly, the system enters the linear growth phase later, and obtains smaller instability growth rate. It means when the curvature of equilibrium current profile is small, the MHD system with viscosity or resistance is more unstable.