| Tokamak,which is able to realize a controllable nuclear fusion with magnetic con-finement,is one of the focuses of current scientific research.The complexity of mag?netically confined plasma have brought many obstacles to the realization of controlled fusion.Anomalous transport in Tokamak and energy transfer between electrons and ions are key physical problems in magnetically confined fusion research.The key to solve the problems lies not only in the continuously improvement of the experimental parameters of fusion devices,identifying problems and solving the problems,but also in the constantly enhancement of diagnostic capabilities.Side by side development through mutual cross-fertilization between theory and experiment is needed in the research.At present,the four-channel poloidal homodyne C02 laser collective scattering system on EAST can simultaneously measure the characteristics of electron mode turbulence with discrete scales in different regions,which provides experimental verification and under-standing for the anomalous electron transport.However,the existing systems can not detect the ion channel turbulence in Tokamak plasma,and there are few direct studies on the cross-scale interaction between electron and ion scales turbulence.Density fluc-tuation of lower wavenumber can be detected through improvement of the diagnostic system.And it is necessary to identify the different components in the detected signals,which are induced by different diamagnetic drifts of electrons and ions.In this paper,an heterodyne C02 laser detect system is constructed base on acousto-optic diffraction and the principle of modern signal processing.Experimental results show that the system can detect frequency shift signals of different amplitudes and directions.Work we have done will be helpful for the upgrade of the homodyne C02 laser coherent scattering diagnostic system on EAST later.The first chapter briefly introduces the crucial importance of the magnetically con-fined fusion.The existence of drift waves in Tokamak is the main reason for the anoma-lous transport.Measuring drift waves at different scales requires developing and im-proving diagnostic techniques.The development of the C02 laser collective scattering system at home and abroad is briefly introduced in this chapter.Realization of a hetero-dyne diagnostic system is needed for the simultaneous measurement of ion and electron turbulence.In the second chapter,firstly,the scattering theory of electromagnetic wave is presented,and the measurement of the microturbulence by collective scattering in the Tokamak is briefly introduced.Secondly,the homodyne C02 laser coherent scattering diagnostic system for electron mode turbulence measurement in EAST is introduced.Realization of a heterodyne diagnostic system elevates the capability for both ion and electron turbulence measurement.In chapter three and chapter four are the hardware setup of the system.Acousto-optic frequency modulation is utilized in the heterodyne system to realize a fixed fre-quency difference between incident laser and reference beam,and the beam transmis-sion strategies are carefully designed to meet the heterodyne detection need.Scatter-ing signal is measured by an infrared photodetector and then processed by a precision preamplifier.Baseband signal is acquired with a differential frequency circuit.Then the high-speed data acquisition card PCI-9812A is used to realize data acquisition and storage based on LabVIEW,which is convenient for subsequent data processing.In the fifth chapter,the calculation of power time-frequency spectrum and the basic theory of wavelet transform are introduced.Wavelet transform of signals is realized with MATLAB,and the difference between wavelet transform and power time-frequency spectrum is presented.Frequency shift signal is generated by multi-frequency acousto-optic diffraction effect,the time-frequency spectrums are calculated and the detection ability of the heterodyne system for frequency shift in different directions is verified.Noise power spectra of the homodyne and the heterodyne systems are calculated,and spectral subtraction methods is used in the noise suppression algorithms.Chapter six summarizes the research results and relevant experience for the future upgrade of the diagnostic system. |
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