Modelling And Optimization Of Plasma Horizontal Displacement Control On The J-TEXT Tokamak

As one of the controlled fusion devices, the tokamak is supposed to create and sustain the plasma with high temperature, high density and long confinement time during the discharge operation in order to acquire positive net fusion energy. According to this, the operation control of the tokamak is particularly important. Generally, the tokamak operation control mainly covers force balance control, plasma current control, plasma density control and the control of the profile parameters. Force balance control, which is one of the basic tokamak operation control tasks, is aiming at controlling the horizontal and vertical displacements and also the shape of the plasma during the routine discharge so as to guarantee the steady operation of the tokamak. J-TEXT (Joint Texas Experimental Tokamak), which is formely known as TEXT-U in Texas University, is a regular medium-sized tokamak device. It could not only produce circular cross-section plasma during discharge, but also achieve a220kA plasma discharge within a300ms pulse length. Due to the circular cross-section and the small elongation the plasma in J-TEXT routine discharge, the vertical instability of the plasma is not apparent. By contrast, plasma horizontal displacement control is more important. The main purpose of the plasma horizontal displacement control is making the plasma reach the desired position in the horizontal direction by adjusting the currents in polodial field coils according to the present plasma horionztal displacement status and its preset position. As a basic and extremely important task, modelling and optimization of plasma horizontal displacement control solidly guarantees the safety, stability and efficiency of the tokamak device and even future fusion reactors.On the basis of the current control requirements and the J-TEXT discharge data in recent years, the manuscript starts from the theory and statistical model, redesigns a cascaded two-loop compound control system for plasma horizontal displacement control, and finally optimizes the new controller. The detailed works are discussed in following contents:According to the historical data of the vertical field (VF), the time delay in the VF power supply control loop (the internal loop) is found and then imported into the updated internal loop model. Taking account of the time delay, a compound controller that combines the feedforward differential signal of the VF presets with the traditional proportional-integral (PI) controller is proposed in the manuscript. By means of the chaos adaptive particle swarm optimization (CAPSO), the parameters of this controller is finely tuned offline which imporves the tracking performance of the internal loop significantly.Considering about the effect of the eddy currents in the passive structure of J-TEXT during routine discharge, the nonlinear kinetic model of the plasma horizontal position control based on the eddy currents is deduced and validated. On the basis of the linear processing of the model, an incomplete derivative PID feedback controller for the plasma horizontal displacement control closed-loop (the outer loop) is redesigned and the response of the outer loop has great improvements. Due to the requirements of the efficiency of discharge preparation and the optimization of discharge operation, the J-TEXT horizontal displacement control simulation platform is built up according to the models of the internal loop and the outer loop.To provide better discharge operating on J-TEXT, the control strategy and the exception handling have been updated by using the historical data. The segments for the discharge are set more accurately compared with the former one. The new strategy has been applied in J-TEXT practical experiment and it is proved that the requirements of the horizontal displacement control for the whole discharge process has been well fulfilled.For the sake of the better suppression of the horizontal displacesment disturbance due to the density sudden change, the manuscript proposes a compound PID controller with a feedforward density compensation part inside according to the statistical result of the numerical relationship between the vertical field and the plasma average density. Practical discharge results show that the import of the feedfoward density compensation apparently quickens the suppression and would not affect the no distinct density change case.