Simulation And Realization Of Divertor Configurations For The J-TEXT Tokamak

The Divertor plays an important role in controlled magnetic confinement fusion device,such as the tokamak.It can avoid the direct contact between the main plasma and the physical materials on the boundary of the device,so as to reduce the impurity sputtering and penetration effectively,and further improve the confinement performance of plasma.It can be said that the divertor configuration is the key point to realize the high confinement mode(H-mode).At present,the popular fusion experiment reactors,such as JET,EAST,HL-2A,DIII-D,KSTAR,ASDEX-Upgrade,all choose the divertor configuration.Tokamak test reactors in future,such as the ITER and CFETR,will also choose the operation mode of divertor configuration.Therefore,the realization of divertor configuration is the basis for solving the key physical and engineering problems of future fusion reactors,and has important strategic significance.In this paper,J-TEXT(Joint Texas EXperimental Tokamak)tokamak has been used as a platform to develop the shape configuration program,and guided by the results given the program,the operation of divertor configuration has been realized for the first time in the experiments on J-TEXT tokamak.The realization of divertor configuration is a great breakthrough on J-TEXT device,which lays a fuoundation for the realization of the H-mode and the study of physical problems related to the fusion reactor in the future.In order to realize the operation and control of divetor configuration on J-TEXT,the related research has been carried out from two aspects of hardware and software,the details are as follows:On the software aspect,two shape configuration reconstruction programs have been established on J-TEXT: equilibrium reconstruction program and current filaments boundary reconstruction program.The magnetic surface distribution of different discharge configurations on J-TEXT has been obtained.For the given equilibrium of different configurations,the last closed flux surface(LCFS)obtained by the fitting mode is consistent with the given equilibrium,and the self-consistency of the equilibrium reconstruction program is verified.The calculation of the fixed boundary equilibrium shows that the external magnetic measurements are not sensitive to the current distribution in the plasma,which provides a basis for the use of the current filaments boundary reconstruction method.The fixed current filaments method was used to reconstruct the boundary of different configurations of J-TEXT,and it was found that the accuracy of the boundary reconstruction by single current filament method under the configuration of the circular cross-section limiter configuration was significantly higher than that of the divertor configuration and the accuracy of the boundary reconstruction of the divertor configuration could be improved by multiple current filaments.The accuracy of boundary reconstruction can be improved by increasing the number of current filaments and decreasing the radius of current filaments distribution.The simulation of the J-TEXT divertor configuration was done by current filaments methods and various factors that may affect the formation of the divertor configuration and the operation regions were explored.The results show that the position of the limiter can obviously affect the formation of the divertor configuration.When the plasma position is close to the high field side,the operating range of the double-null divertor configuration is large,and when the plasma position is close to the low field side,the operating range of the middle single-null divertor configuration is large.The parameters of power supply of the divertor coils were determined and an idea was provided for the control strategy of J-TEXT by the simulation of the divertor configuration on J-TEXT tokamak.On the hardware aspect,there are mainly two aspects: the construction of the target plate and the construction of the hardware for the determination of the configuration.The x-point of J-TEXT tokamak divertor configuration is located at the high-field side,and the strike points are on the high-field side.In order to avoid damage to the first wall of the device,the graphite target plate is completely covered on the high-field side of the vacuum vessel.In terms of diagnostics,a rectangular array of magnetic probes for configuration reconstruction is constructed.This array consists of 26 two-dimensional magnetic probes distributed on the walls of the vacuum vessel.The effective area of the probes is calibrated by Helmholtz coils.In addition,a plasma position measurements probes and a diamagnetic measureent system are built.The position probes can be used for the measurement and the control of the plasma position and the diamagnetic measurement compensates the effect of current diffusion in TF coils of J-TEXT,and can be used to measure the plasma stored energy,the poloidal beta and the energy confiment time.After the completion of target plate,power supply,diagnostics and other subsystems,and after debugging,the discharge of the high-field side middle single-null divertor configuration was successfully realized on J-TEXT,preliminary experiment results were obtained and analyzed based on the equilibrium reconstruction program.The experiments of high density discharge and ECRH heating were carried out under the middle single-null divertor configuration,and some typical shots were obtained.