Real-time Monitoring,Control And Protection Of Vertical Displacement Event On EAST

Plasma vertical instability is one of the main characteristics of elongated tokamak plasmas.Due to loss of plasma vertical control,resulting plasma disruption,can bring huge electromagnetic forces and head loads to tokamak.EAST has elongated plasma configuration,similar to ITER.Therefore,reliable control of vertical instability is necessary for EAST operation.There are no real-time monitoring of plasma vertical growth rate and practical applications of plasma disruption prevention and safe shutdown in worldwide tokamak devices,including EAST.Therefore,it is imperative to carry out this research on EAST as soon as possible.Factors affecting tokamak plasma vertical instability,include plasma current distribution,magnetic surface structure,passive conductor structure surrounding plasma(i.e.,vacuum chamber and first wall components),and the active control coil system for this instability.In this thesis,TOK-SYS tool developed by D?-D plasma control team is used to establish vertical control system model including vacuum chamber,first wall components,coil system and the plasma,based on rigid plasma response model,so that vertical growth rate of EAST typical configuration can be calculated.In order to accelerate calculation to satisfy real-time requirements of plasma control system,TOK-SYS tool is rewritten using C and CUD A programming languages,and the parallel calculation of plasma vertical growth rate can be carried out.Besides,calculation results are consistent with results of TOK-SYS tool.The calculation time of one parallel vertical growth rate is about 2 ms,which meets the need of real-time monitoring of vertical growth rate.In order to monitor vertical growth rate in real time,the above parallel calculation should be carried out in real time,by integrating with plasma control system(PCS).By using data-sharing technology,plasma magnetic diagnostics can be transmitted from PCS to a GPU computing system.Next,plasma vertical control system can be modelled using rigid plasma response model,based on plasma equilibrium(such as spatial distribution of plasma current)reconstructed by PEFIT,and the passive structural model.Finally,value of vertical growth rate can be calculated in the GPU computing system and sent to PCS immediately.The experimental results show that total system overhead time during one control cycle is about 1.1 ms,so that real-time monitoring of vertical instability is realized.The real-time monitoring of vertical growth rate was applied in EAST and D?-D joint experiment as well(#95142-95145).Capability of plasma vertical control system is limited,therefore when plasma vertical growth rate exceeds controllability,it will inevitably lead to plasma disruption.During plasma discharge,the risk of plasma disruption can be greatly reduced by controlling vertical growth rate in real time.In this thesis,a real-time method to change plasma elongation is proposed to control evolution of vertical growth rate.A new control algorithm is added in EAST PCS by using PID controller,which works with the ISOFLUX/PFFIT shape control algorithm,and finally formulates closed-loop feedback control module of vertical growth rate(i.e.,gamma controller).In the EAST experiment(#91129-91131)in 2019,experiments for decreasing vertical growth rate are carried out using this gamma controller,and the effectiveness of gamma controller is verified.Once plasma vertical instability is nearly loss of control,it is necessary to find a reliable and safe way to shut down tokamak device.However,such an event-driven plasma soft landing method has not been developed in tokamak devices in the world.In this thesis,a plasma vertical instability event driven soft landing control algorithm is proposed.Once vertical growth rate exceeds a certain threshold value,a soft landing control strategy will be triggered to decrease plasma current at a certain predetermined safe rate,while maintaining a certain plasma configuration.This abnormal shutdown algorithm is developed in PCS,and effectiveness of the algorithm is verified in the EAST experiment in 2019(#85512).Once control of plasma vertical instability is lost,serious damage caused by disruption must be mitigated immediately.For this reason,a vertical instability exception event processing algorithm is added to EAST PCS.Once one of the values(i.e.,values of plasma vertical growth rate,absolute vertical displacement and deviation of vertical control),reaches a certain threshold,this abnormal shutdown protection action of massive gas injection(MGI)will be triggered.Results during fall of 2019 EAST experiment proves the reliability of this algorithm.The development of monitoring,safety shutdown and protection methods of plasma vertical instability,is significant for decreasing the damage of vertical unstable disruption,which is one of the main types of plasma disruptions for future EAST high-performance operation.Such a development can also provide practical experience for future large tokamak device,such as ITER,CFETR.