Construction Of The Magnet Power Supply System On The NCST Spherical Tokamak Device

Spherical Tokamak is a magnetic confinement fusion device with an outstanding low aspect ratio.The installation of Nan Chang Spherical Tokamak(NCST)and its periphery debugging were completed in 2020,and the experimental goal of the device is to obtain a plasma current of 100 k A with a discharge time of 100 ms.Meanwhile,the important goal of the device is to initiate plasma currents by utilizing merging compression.The spherical tokamak is very conducive to teaching and research at the university due to its main advantages of relatively low cost,relatively simple technology,and quick response to new ideas and concepts.The magnet power supply system is an important component for a spherical tokamak and is used to energize the magnets of the spherical tokamak device.At present,there are five power supply systems in the NCST device,which are the toroidal field power supply,ohmic field power supply,merging compression power supply,and two equilibrium field power supply systems.In the thesis,the NCST device magnet power system is analyzed and the more vulnerable components of the circuit structure are protected.Based on the NCST magnet system,the five power supply systems were tested individually,and the stability of the power supply systems could meet the NCST device experiments.According to the test results,the voltage setting parameters of the capacitor bank for different current levels of each magnet coil were determined,and the current levels of each magnet coil met the expected targets.During the initial discharge of a tokamak device,the field null configuration is one of the critical conditions for Ohmic breakdown.The coupling between the magnets of the NCST device was more obvious,and the field null configuration was damaged in the plasma experiments.A more economical improvement scheme was proposed and implemented,which alleviated the coupling phenomenon to some extent,by analyzing the power supply system of the equilibrium field.Meanwhile,in order to realize the experiments of microwave system assisted ohmic start-up on the NCST device,two improvements are proposed in the thesis: on the one hand,the soft connection of the toroidal field magnets is modified to reduce the stray field caused by the flexible connection;on the other hand,the balance field PF5-PF6 power supply system is improved to increase the capability of the equilibrium field.Finally,the plasma experimental results were significantly improved,and the stability,flexibility and reliability of the power supply system of the NCST device were verified,which laid a solid foundation for obtaining better plasma experimental results next.