Design Of Power Supply System And Numerical Studies On Resistive Wall Mode In KTX

The Keda Torus eXperiment(KTX)is a new reversed field pinch(RFP)device with a major radius of R=1.4m and a minor radius of a=0.4m.The first KTXplasma was successfully produced in August,2015.This thesis reports the design ofpower supply system and the numerical studies on resistive wall mode in the toroidalmagnetic fusion device relevant to the KTX parameter regime and configuration.Theprimary goal is to provide the physics and theory bases for the prediction of dischargewaveforms,the design of a power supply feedback control system,and the control ofplasma equilibirum and resistive wall modes in KTX.Firstly,a poloidal and toroidal magnetic field coupling circuit model is developedto simulate discharge waveforms of the KTX RFP to ensure that the design of the powersupply systems is able to achieve the typical discharge parameters.The radial profiles ofplasma current density and magnetic field used in the coupling model are characterizedby the modified Bessel function model(MBFM)derived from the well-known Taylor'stheory.The power balance in the energy conservation of poloidal and toroidal fields isused to establish the connection between these two fields.The numerical solutions ofthe coupling show that the KTX power supply system is capable of achieving the de-signed discharge parameters,such as field reversal parameter(F),pinch parameter((?)),magnetic field,plasma current and loop voltage.Furthermore,the delay of magneticfield penetration due to the effect of vacuum vessel is also considered in the model.Secondly,an equilibrium field power supply(EQPS)circuit using a feedback H-bridge pulse width modulation controller has been developed to control the plasma hor-izontal position and to satisfy the requirement of RFP plasma equilibrium in the KTX.Results from simulations of plasma discharge aimed at achieving plasma equilibriumdemonstrate the success of the power supply circuit design.Additionally,this designprovides a feasible control solution for achieving equilibrium conditions in future KTXpower supply upgrades.The main goal of this study is to provide a simple,effective,and economically viable solution for a feedback control system for an EQPS to achievethe plasma equilibrium.Thirdly,the linear instablity of resistive wall mode(RWM)in KTX has been num-rically investigated.This study involves two parts.(1)The benchmark studies ofNIMROD code for RWMs are performed in cylindrical tokamak geometry.NIMRODcode is also employed for exploring the toroidal effects on tokamak RWMs in differentaspect-ratios.(2)The standard formulation of dispersion relation for RWM based onthe MHD energy principle has been evaluated for a cylindrical ?-(?)0 model of KTX RFP plasma equilibrium,in an effort to investigate the effects of thin shell on the RWM in KTX.Full MHD calculations of the linear RWM in KTX using the NIMROD code are also being developed.The detailed comparisons between theoretical analysis and NIMROD calculation results are presented and discussed.