| Our team has developed multiple microwave reflectometry diagnostic systems on EAST tokamak, including a set of integrated profile reflectometry and a multichannel millimeter-wave fluctuation diagnostic system at K port, as well as, a Doppler reflec-trometry system above and below the middle plane of tokamka at O port. This paper focus on the upgrade of the Doppler reflectrometry (the hardware of the poloidal corre-lation reflectometry), the GAM in the edge of plasma and others edge coherence mode,especially a symmetrical electromagnetic oscillation, which appear near the X point of plasma. Finally, the effects of the perpendicular velocity gradient on Doppler system also been studied.The system at O port composed of two independent X-mode Doppler system(Q-band and V-band system) before upgrade. With the increase of field parameters of EAST, the Q-band system has been unable to measure the cut-off layer inside LCFS. So we have developed a V-band poloidal correlation reflectometry, which can been used to measure the long-distance coherence mode, such as GAM,which play a very import role in regulating the turbulence and enhancing the confinement. Over the last decade,it is has been recognized that zonal flows are themselves nonlinearly driven by the tur-bulence, in their turn can influence the turbulence fluctuations and anomalous transport.Based on the poloidal correlation reflectometry, we have studied the magnetic fluctuations fluctions of GAM for the first time on EAST tokemak. It observed that the poloidal component and toroidal component of magnetic field perturbation have poloidal wave number m=2 and n=0. The radial component and poloidal component have a 0 and ? cross-phase near the upper divertor and lower dicertor. That measure-ments are consistent with the theory result. we also found an electromagnetic model with a center frequency of 7-10kHz. The magnetic field oscillations satisfy the struc-ture of m = 1 and n = 0, which is the strongest near the X point. That shows that the oscillations maybe a instability mode,which caused by the low Z impurity radiation.A novel method also been developed to solve the Doppler frequency shift by sep-arating the forward scattering and backscattering components though the cross-phase spectrum between I-signal and Q-signal from quadrature mixer, based on the differ-ence of symmetrical characteristic between forward scattering and backscattering signal spectrum.It is proven that this method is more effective than the tradition approached such as the Multiple Signal Classification (MUSIC), Fast Fourier Transformation (FFT),Gaussian fitting of the spectrum for receiced signal with forward scattering.Finally, we also studied the effect of the velocity gradient on Doppler power spec-trum with 2D FDTD. The numerical results show that the Doppler backscattering mainly occurs around the cut-off layer, and that it has a linear response to turbulence when the fluctuation level is low. However, at higher density fluctuation levels, nonlinear effects become important, and the influence of the area outside the cut-off layer be-comes significant. The velocity gradient causes the backscattering spectrum to become non-Gaussian and asymmetrical; this effect has also been noticed in experiments in the Experimental Advanced Superconducting Tokamak (EAST). |
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