Optimization Of Island Divertor Configuration And Divertor Heat Load Distribution In Magnetic Confinement Fusion Plasma

For high-performance,high-power,long-pulse plasma operation,the peak heat load on divertor target is a key issue to be solved in ITER and future magnetic-confinement fusion reactors.A large number of studies have confirmed that the peak divertor heat load far exceeds the existing material tolerance level in the future fusion reactor,and the larger plasma current,the smaller power decay length of scrape-off layer(SOL),the more peak heat load on divertor target.Therefore,how to decouple the nonlinear interaction between divertor heat load and plasma current is the key to solve the problem of peak heat load on divertor target.Compared with poloidal divertor configuration in tokamak,island divertor configuration in stellarator has a weaker correlation with plasma current,which contributes to more uniformly distributed heat load and being also easier to enter stable detachment of divertor operation.Thus,it is expected to be one of the effective means to solve the problem of peak heat load on divertor target.Based on the above advantages of island divertor,it is of great importance to introduce it into tokamak to carry out relevant research and explore its application in tokamak.In this thesis,the simulation and experimental studies on the optimization of island divertor configuration and divertor heat load distribution are carried out on the W7-X stellarator in Germany and the J-TEXT tokamak in China,respectively.On W7-X,the magnetic topologies of the island divertor configuration under different plasma three-dimensional equilibrium responses are investigated with the help of the 3D equilibrium code HINT,and it is found that the plasma beta effects have a strong dependence on magnetic configuration.On the one hand,it can enhance stochastization of field lines in the standard configuration,the high-mirror configuration and the high-iota configuration,On the other hand,it’s able to make the self-healing effect of edge n/m = 5/6(n and m are the toroidal and poloidal mode number,respectively)magnetic islands in the low-iota configuration.By comparing three-dimensional magnetic topologies under different plasma pressure profiles,it is demonstrated that the volume-averaged plasma beta plays a more important role in edge stochastization and self-healing effects of magnetic island compared to the on-axis plasma beta.It is also revealed that plasma toroidal current can reduce edge stochastization.In the study of divertor heat load distribution,a Monte Carlo transport model based on anisotropic diffusion is introduced to improve the accuracy and convenience of divertor heat load estimation.Based on the above three-dimensional equilibrium magnetic field and heat load estimation model,it is demonstrated that plasma beta effects can increase the wetted area for divertor heat load deposition,which explains the reason why the divertor wetted area is proportional to the power flowing into the scrape-off layer.These results demonstrate that magnetic topology and plasma transport can have a significant impact on the divertor heat load distribution.On J-TEXT,the existing resonant magnetic perturbation(RMP)syatem is used to prestudy the m/n = 3/1 island divertor and explore the construction scheme of island divertor configuration on tokamak by increasing plasma current and decreasing edge safety factor to make edge islands intersecting with divertor target,so as to construct island divertor.The experimental study of excitation thresholds of 3/1 magnetic island reveals that the magnetic field spectrum of the existing RMP coil is impure,which is easy to excite 2/1 locked mode and is not conducive to the expansion of the operation range of the 3/1 island divertor.According to construction requirements of island divertor on J-TEXT and the problems in the pre-study experiments,m/n = 4/1 is selected as the dominant magnetic component of island divertor coils.In order to improve the purity of magnetic spectrum,an innovative method is proposed to design the coil structure based on tilt angle of field lines.After the engineering installation and experimental testing of island divertor coil,the formation of the4/1 island divertor configuration is explored.It is initially found that the 4/1 island divertor configuration has the effect of reducing the peak heat load on divertor target.In this thesis,the effects of three-dimensional equilibrium plasma responses on the magnetic topology of island divertor and the divertor heat load distribution are investigated in the W7-X stellarator,which provides a strong support for the realization of highperformance and long-pulse plasma operation in W7-X and provides an important reference for the design of future stellarator fusion reactors.Besides,the island divertor coils are designed in the J-TEXT tokamak to verify the feasibility of the formation of island divertor configuration in tokamak,which provides a new solution for the optimization of divertor heat load distribution in future tokamak fusion reactors.In addition,the research in this paper spans two types of magnetic confinement devices,including stallarator and tokamak,and has important reference value for the optimization of advanced magnetic configuration in future fusion reactors.