Error Field Active Feedback Control Experimental Research And Minor Disruption Prediction On KTX

Nuclear energy is the best way to solve the human energy issue.In view of the problems brought by the decommissioning of nuclear fission facilities and the recovery of nuclear waste,the study of reverse field pinch(RFP)magnetic confinement fusion has important physical meaning and broad future to make a break through in nuclear fusion power generation technology and world energy picture.Keda Torus eXperiment(KTX)magnetic confinement fusion experimental device is the first RFP device in China,which was developed independently.The development of active feedback control system in RFP configuration can restrain error field and plasma instability,prolong discharge time,improve plasma quality and confinement performance.KTX active feedback control system is designed for error field active feedback control at the vertical gap.The aim is to achieve three-dimensional plasma control,improve plasma quality and energy restraint time together with saddle active control system.The system consists of four parts:electromagnetic probe array,field programmable logic gate array(FPGA),linear power amplifier and active control coil array.The active control coil array is used to generate local radial disturbed magnetic field(Br)at the northern and southern vertical gap to suppress the development of local error field.During the discharge,plasma current gravity center deviates from the center of circular section to the low field side continuously until the plasma quenches.In the experiment with 40KA plasma current,the error field active control system generates a 100 Gauss local vertical field through the active control coil array at the gap,which weakens the local error field intensity,inhibits the tendency of plasma moving towards the low field side,increases the plasma current by 50%and prolong discharge time by 30%.The plasma disruption phenomenon is a common physical phenomenon in magnetic confinement fusion devices,but its causes are complex.Such as the temperature limit,density limit,halo current and many other reason can cause the plasma disruption.In Tokamak,large plasma disruption is often accompanied by plasma current quench,hot electron escape and internal wall burning,and other consequences.Due to the existence of conducting shell,there is no large plasma disruption in RFP device theoretically.However,the minor plasma disruption phenomena would be caused by the interaction between current and conducting shell.In the KTX discharge experiment,minor plasma disruption occurs frequently,and closely related to the parameters such as plasma current gravity center displacement and electron temperature.By means of machine learning and plasma diagnostic methods like boundary electromagnetic probe array,soft X-ray and H-alpha spectrum,the development mechanism of KTX minor plasma disruption is improved and the prediction is realized 200 microseconds ahead of KTX minor plasma disruption happened.