Experimental Study On Edge Plasma Dynamic Behavior By A Semi-tangential VUVI System Developed On EAST

The edge plasma behavior plays an important role in the global confinement of tokamak plasma.In order to further research the dynamic behavior of tokamak edge plasma,it is necessary to develop targeted diagnostic with high spatial and temporal resolution.In this paper,the hardware of high-speed VUVI diagnosis was upgraded on the EAST device.Experimental study of edge plasma dynamics process such as ELM dynamic and dust grain ablation process by using upgraded VUVI diagnostic system.A vacuum ultraviolet diagnostic(VUVI)system was developed to measure the two-dimensional radiation fluctuation information of the plasma at the edge/pedestal area of the EAST.The image data obtained from the diagnosis can be used to extract the physical information of edge plasma fluctuation structure and its dynamic evolution process.In this paper,the filament structures generated during the ELM burst were obtained by using SVD decomposition method and video data reconstruction.And the toroidal and poloidal characteristics of the ELM filament and their dynamic evolution process were studied.The results show that the poloidal width of the ELM filament presents different characteristics at different stages of ELM burst.,the poloidal width of the ELM filament increases at the rise phase of VUVI signal;the poloidal width of the ELM filament decreases at the decay phase of VUVI signal.In addition,The pitch angle derived from the VUVI imaging data agrees well with that calculated by the EFIT code.The poloidal velocity shows no obvious change during the rise and decay phases in an ELM crash.In addition,both the poloidal width and the poloidal velocity of the filament increase with the heating power.We have observed a clear ablation process of dust grain using the upgraded VUVI diagnosis,and a preliminary analysis of the dust particles dynamic.During the ablation process of dust particles,the ionized dust will be elongated along the direction of the magnetic field line,and appear asymmetry in the direction of the perpendicular magnetic field line.The secondary filamentous ablation cloud structure appears on the side with high density.Obvious corrugated structure and its propagation process can be seen on the video data.The speed of dust grain in the ablation process is anisotropic,and the speed of the secondary filamentous ablation cloud structure generated by dust grain ablation in the direction of the perpendicular magnetic field line is about 150 m/s.Preliminary analysis shows that the velocity of the dust particles in the ablation process is different in different directions,and the velocity of the secondary filamentous ablation cloud structure is about 150 m/s along the vertical direction of the magnetic field line.In addition,dust particles will split during the ablation process.The above process has important reference significance for perfecting the impurity ablation model in the process of projectile injection.In addition,through the hardware upgrade of the diagnostic system,the system signal-to-noise ratio has been significantly improved,and the system data storage speed and stability have also been greatly improved,which provides a good data guarantee for the completion of the work of this paper.