Simulation Of Poloidal Field System And Quasi-Single Helicity In KTX Reversed Field Pinch

The KTX (Keda Torus eXperiment) is the first large reversed field pinch (RFP)device under design and construction at the University of Science and Technology of China. This thesis mainly studies the discharge simulation of KTX, which is based on the equivalent electrical circuit and power balance model. The 3D full MHD code NIMROD has been used to analysis the MHD instability and the possibilities of achieve Quasi-Single Helicity(QSH) in the KTX regimes.Firstly, the radial equilibrium of the toroidal plasma is maintained by the vertical field which is produced by the equilibrium field coils. The equilibrium is also affected by the eddy current, which is generated by the coupling of copper shell, plasma and poloidal field coils. An equivalent circuit model is developed to analyze the dynam-ic performance of equilibrium field coils, without auxiliary power input to equilibrium field coils and passive conductors. Considering the coupling of poloidal field coils, cop-per shell and plasma, the evolution of spatial distribution of the eddy current density on the copper shell is estimated by finite element to analyze the effect of shell to balance during the KTX operation. The simulation results show that the copper shell and equi-librium field coils can provide enough vertical field to balance 1 MA plasma current in phase 1 of a KTX discharge. Auxiliary power supply on the EQ coils is necessary to control the horizontal displacement of KTX due to the finite resistance effect of the shell.Secondly, the KTX discharge mode is established, which based on the α-(?)0 equi-librium model and the principle of power balance. The PPCD power supply parameters has been estimated. Considering the magnetic flux consumption in vacuum zone be-tween stability shell and toroidal field coils, as well as exist the shielding effect for passive conductor shell, therefore, the PPCD power parameter more bigger than MST device, corresponding on the more harsh properties of PPCD power requirements. The simulation results show that the vacuum vessel should be as thin as possible, and the toroidal field coils also should be as near to the vacuum vessel as possible during design device, since it can reduce the cost of PPCD auxiliary power.Finally, focus on the research key of RFP——3D QSH state. The appearance of the QSH state reduces magnetic fluctuations and improves the RFP confinement, es-pecially for the SHAx state, which has an inner electron temperature transport barrier and relatively wide hot helical core. The potential formation of the QSH state in the KTX is investigated in resistive MHD simulations using the NIMROD code. We focus on the effects of finite resistivity on the mode structure and characteristics of the domi-nant linear and nonlinear resistive tearing-mode in a finite β, cylindrical configuration of reversed field pinch model for KTX. In the typical resistive regimes of KTX where Lundquist number S=5×104, the plasma transitions to a steady QSH state after e-volving through an initial transient phase with multiple helicities. The dominant mode of the QSH state develops from the dominant m=1 linear tearing mode instability. Our simulation suggests that β is an important parameter for the formation of the QSH state in the KTX configuration and parameter regimes. In lower (3 regime, the QSH state are intermittent and short in duration; in higher (3 regime, the QSH state persists for a longer time and should be more observable in experiment.