Investigation Of Three-dimensional Distribution Of Plasma At The Edge Of J-TEXT Tokamak

The toroidal magnetic field ripple,magnetic island and externally applied resonant magnetic perturbation(RMP)can destroy the toroidal symmetry of magnetic filed and then cause the three-dimensional(3D)magnetic field effect.Previous research have shown that the 3D effect has a great impact on the plasma confinement performance,but its physical mechanism has not yet been unified.Therefore,systematical study on the 3D effect on plasma is of great significance for improving the confinement performance.In this thesis,we investigate the turbulent transport in the edge plasma under 3D magnetic field on J-TEXT tokamak.Firstly,a set of limiter target electrostatic measurement system has been established to meet the diagnostic needs of the experiment.The system consists of a limiter poloidal Langmuir probe array and a limiter current monitoring system.The probe array is a rectangular array which consists of 54 probes embedded in the graphite tile of the limiters for measuring plasma parameters.The current monitoring system consists of five Hall sensors which used for detecting the current of the movable limiters and the north(south)vacuum walls respectively.Secondly,the turbulence transport under two 3D magnetic field configurations has been studied,including spontaneously rotating magnetic island and externally applied static RMP.It shows that the edge electrostatic fluctuation is modulated by the core 2/1 rotating island,so it has the same spatial mode as the island.The phase shift of electrostatic fluctuation in radial direction indicates that the modulated turbulent transport may also effect the edge electrostatic fluctuation,besides the effect of the modified magnetic geometry by island.Experiments with 3/1 static RMP show that both the RMP amplitude and phase have great influence on the edge turbulence.A small RMP current(2kA)significantly enhances the turbulence near the resonance surface,and increases the local cross-field transport.However,in the case of a larger RMP current(3/4kA),the turbulence properties will change significantly due to the formation of static island after RMP penetration: the dominant components of turbulence change from high frequency to low frequency,the zonal flow and GAM are destroyed,and a beta-induced Alfvén Eigenmode(BAE)like mode is excited around island.By comparing the turbulence near the X-and O-point of island,it’s found that the turbulence is mainly concentrated at the X-point.Similarly,the particle flux at X-point is much larger than O-point,and mainly distributes in the inner side of the separatrix of island.The experiment suggests that the edge island can be as a tool to improve edge plasma confinement.