An Experimental Study On Pedestal Turbulence In The Edge Of Plasma On EAST Tokamak

Operation in diverted H-mode is the foreseen scenario for next step tokamak fu-sion devices,e.g.for the China Fusion Engineering Test Reactor and ITER.H-mode is characterized by spontaneous formation of a narrow region with step-like profiles and steep gradients at the plasma edge.The pedestal is a crucial factor which decides the intergral performance of the plasmas.On the one hand,the temperature in pedestal de-cides the temperature of core plasma because the stiffness of core plasma.One the other hand,the parameter of pedestal influences the size of ELMs and hence the lifetime of fusion materials.So it means a lot to study about pedestal physics.The improvement in confinement in the H-mode is due to suppression of turbulence in the plasma edge region.However,both the experimental and the Gyro-kinetic simulation results indicate that turbulences is still abundant in the H-mode.The turbulence is excited as the steepen gradient of pressure pedestal forms,the turbulence coud in return limit the further in-creasing of pressure of pedestal.The results of experiments and simulations indicate that the turbulence could influence the process of particle as well as heat flux trans-port.Hence the pedestal turbulence in H-mode remains a heat topic in the area of toka-mak transport nowadays.There're many diagnosics employed for the observation of pedestal turbulence.The Doppler reflectometry can be used to measure Doppler shift,density fluctuations and poloidal velocity fluctuations in a narrow region owing to its high spatial and temporal resolution.This paper mainly introduces a series of work on the measurement of H-mode turbulence in pedestal,which is divided into the following three parts:(1)Developement of Doppler systems.In EAST Tokamak,two sets of Doppler systems,including 6-channel Doppler reflectometry and 4-channel Doppler reflectom-etry,have been developed for the measurement of pedestal turbulence.The 6-channel Doppler reflectometry was put into EAST experiments in 2017.They are located below the middle plane of the K-port parallel to the middle plane with 0.16m poloidal separa-tion.The incident angle is determined by the plasma configuration.The wavenumber range is?4-7cm-1.By the 6-channel reflectometry we observed the geodesic acous-tic mode(GAM)in the pedestal of H-mode on EAST tokamak,and we firstly confirmed the m=1 structure of GAM's magnetic fluctuations in the experiment.Result shows that the m = 1 component of GAM's magnetic component would become dominant than the m=2 during H-mode.Based on Doppler measurements,we believe that the deeper radial electric field during H mode accouts for this phenomenon,which is con-sistent with the theoretical prediction.We also find that the GAM cound modulate the envelope of ambient turbulence(AT),which implies the causal relation between radial electric field Er oscillation of GAM and the AT.Besides,the four-channel one was de-veloped in K-port in 2019.It is located above the mid-plane at 0.175m and obliquely incident at an angle of-15°.In Chapter 2,we present the measurement of key mi-crowave devices of the four-channel Doppler reflectometry.The test results show that the four-channel Doppler reflectometry has a well response to low-frequency velocity fluctuation in the laboratory.Experimental results on EAST verify the feasibility of the 4-channel reflectometry system.(2)Study of turbulence/instability which influences the transport by the interaction.We studied the multi-scale interaction between the n = 1 external kink mode and the n = 12-17 coherent mode(CM)by means of different diagnostics(POINT,ECE,XUV)on EAST tokamak.It is found that the kink mode could interact with CM in two ways.The first way is that the n= 1 mode could change the temperature gradient and consequently modulate the amplitude of the gradient-driven CM.The other way is the directly non-linear interaction between n = 1 mode and the n = 12-17 CM.In addition,the results show that the multi-scale modulation does not change the structure of the pedestal.(3)Turbulence in the H-mode pedestal(SOL)region contributes to particle trans-port.A high-frequency electromagnetic mode(HFM,100kHz<f<400kHz)is reported,which can both be observed in the pedestal region and the SOL during the type-? ELMy H-mode discharge.In SOL,the HFM propagates in the electron dia-magnetic direction in both the laboratory frame(22km/s)and plasma frame(24km/s)with m(?)28,n?8,k?pi?0.04.Direct measurement shows that the HFM can drive inward particle flux,which can be explained by the electron diamagnetic rotation of the HFM.The time evolutions of particle flux driven by the low frequency turbulence(LFT,or 'blobby' structures)and the HFM as well as the typical decay length of di-vertor particle flux suggest that the decay length in SOL can both be modified by the outward particle transport of the 'blobby' structures(?r,LFT,f<40kHz)and inward particle transport by the HFM(?r,HFM).The decay length of the particle flux is mostly suppressed when a significant inward flux by the HFM bursts under the condition of a low-level outward flux by 'blobby' events,suggesting the important role of anomalous transport on the decay length in the SOL.