Development And Application Of Poloidal Correlation Reflectometry To Study Turbulent Structures On The EAST Tokamak

One of the key issues of magnetic confinement fusion research is the anomalous plasma transport.During which,micro-scale drift wave turbulence was considered as the major mechanism underlying such an anomalous transport.Meanwhile,the interaction between the micro-scale turbulence and meso-scale instabilities could significantly influence the transportation of particles and energy.Understanding the features and the associated dynamic process are beneficial to the mechanism of the turbulent transport,so as to optimize the performance and confinement of the plasma.To this end a deeper understanding of the mechanisms controlling the development,saturation and stabilization of turbulence is needed.The experimental observation of turbulence is the prerequisite for conducting further research,a main challenge in these investigations is the measurement of plasma parameters on both small temporal(?s)and spatial(mm)scales.Poloidal correlation reflectometer is a technique based on the reflection of microwave with higher temporal and spatial resolutions.The arrangement of multiple receiving antenna array can not only measure localized turbulence,but also analyze the spatial structure of turbulence.Further more,It is also possible to measure the rotation velocity of plasma and its shear under certain assumptions,thus,the radial electric field and its shear.Those quantities are of significant role for further physical analysis.The thesis is done on the devices of EAST tokamak and Wendelstein 7-X stellarator.The thesis discuss the development of a poloidal correlation reflectometer system and the related physical research?An O-mode polarized(multiple fixed frequency points,20.4GHz,24.8GHz,33GHz,40GHz)poloidal correlation reflectometer was developed firstly on EAST.The cut-off density of this system is only related to the plasma electron density,so it is not affected by the variation of confinement magnetic field during the operation of EAST.The development of the diagnostic includes the design of microwave diagram,the selection of microwave sources,the arrangement of antenna arrays,and the data acquisition and control system.The performance of the system is optimized by testing key microwave components.The system has been used to measure the turbulence behaviors during the the EAST experimental campaign since the completion of the assemble and test.The low frequency oscillation in pedestal region which is rarely reported before is investigated under the measurements of the the O-mode reflectometer.This low-frequency coherent oscillation has a structure of toroidal number(n=0),indicating an axisymmetric mode,while its poloidal magnetic structure demonstrates an m=1 standing wave with in-out asymmetry.The pedestal turbulence,density profile and particle flux onto the divertor are modulated by this low-frequency mode.During the suppression of low frequency turbulence(<400kHz),a high-frequency turbulence(>500kHz)appears.Further analysis shows that the appearance of this high-frequency turbulence is accompanied with the saturation of the pedestal temperature,that is,it has the characteristics of micro-tearing mode turbulence,can drive outward heat flux transport.During the island divertor experiments of W7-X,with the measurements of the poloidal correlation reflectometer,the low frequency fluctuations which exists outside the last closed flux surface,in the scrape off layer and the remnant island is investigated.Similar with the EAST result,this low-frequency mode shows clearly modulation effect on the background turbulence.Meanwhile,further study found that the low-frequency coherent fluctuations can also modulate the plasma poloidal flow.The dependence of this low-frequency coherent fluctuation on plasma parameters is studied.The low frequency fluctuation can be stimulated by increasing the heating power and variation of edge magnetic topology.However,the detailed dynamic process of this dependency needs further studies.This thesis studies the low-frequency coherent oscillations in different types of devices and different confinement regimes based on the measurements of poloidal correlation reflectometer.Studies have shown that this low-frequency coherent oscillation can significantly modulate turbulence and plasma flow.It is of great significance for studying the physical problems related to the interaction between macroscopic instability and microscopic turbulence.