Development Of Multi-channel Doppler Reflectometer System And Related Experimental Research On J-TEXT Tokamak

The edge turbulent transport in tokamak plasma is not conducive to the improvement of plasma confinement performance.Therefore,understanding the edge turbulence and transport mechanism is very important for the study of magnetic confinement fusion.The multi-channel Doppler reflectometer is an important diagnostic for turbulence research in tokamak.It has the advantage of simultaneously observing the plasma turbulence in several radial positions with high temporal and spatial resolution and high wavenumber resolution.In this thesis,a multi-channel Doppler reflectometer system has been developed,which consists of two parts:U-band fixed-frequency multi-channel system and V-band variable-frequency multi-channel system.This thesis mainly focuses on the development of multi-channel Doppler reflectometer and related physical experiment results.The thesis mainly introduces the development of multi-channel Doppler reflectometer system,including frequency band selection,generator array design,intermediate frequency demodulation system,acquisition system and layout.The fixed-frequency multi-channel Doppler reflectometer on J-TEXT adopts a microwave source scheme based on a filtered phase-locked loop to generate a series of frequency points with similar power,covering 40-57.5GHz（U-band）,and the frequency spacing is 2.5GHz;The variable frequency multi-channel Doppler reflectometer uses the combined output scheme of the synthesized source after frequency multiplication,and realizes the flexible adjustment of the observation range in the V band（50-75GHz）by remotely controlling the output frequency and power of the synthesized source.The IF demodulation system guarantees the normal IQ signal by setting the attenuation value of the adjustable attenuator.The Doppler signal sampling rate is 5MHz,the signal spatial resolution is1～2cm,the detection wave number of the fixed frequency system is2-10cm^-1,the detection wave number of the variable frequency system is4-12cm^-1,and the system performance is tested,mainly including the RF filter test and the generator array test,IQ signal test and system platform test.The reliability of the multi-channel Doppler reflectometer system has been confirmed.This thesis also introduces the data processing method of Doppler signal,including the ray tracing simulation,density fluctuation analysis,Doppler frequency shift analysis and bispectrum analysis.In the density fluctuation analysis,the influence of electron cyclotron heating（ECRH）on the relative density fluctuation was observed,and it was found that the signal power spectrum broadened,and the high frequency components increased.In the Doppler frequency shift analysis,the Doppler frequency shift is used to calculate the perpendicular turbulence propagation velocity and radial electric field.Using bispectral calculation and analysis of Doppler signal,the existence of geodetic acoustic mode（GAM）is confirmed.Based on this set of multi-channel Doppler reflectometer system,related physical experimental researchs have been carried out,mainly including the observation of the zonal flow and the influence of the resonance magnetic perturbation field（RMP）on the edge turbulence.Through the phase disturbance analysis in the J-TEXT experiment,GAM was observed in the J-TEXT boundary region,its frequency gradually decreased radially outward,and its amplitude increased.It is found that the GAM frequency will increase under ECRH,and the appearance of m/n=2/1 magnetic islands can suppress GAM.In the experiment of the external perturbation field,it is found that the m/n=2/1 static perturbation field can change the distribution of the edge plasma turbulent perpendicular turbulence propagation velocity,density fluctuation,and even GAM when it penetrates.There is almost no effect when it is not penetrated.Dynamic RMP also does not change the perpendicular turbulence propagation velocity distribution of the edge plasma,but it will increase the perpendicular turbulence propagation velocity fluctuations.In summary,this thesis has completed the development of the J-TEXT multi-channel Doppler reflectometer system and put it into use,and obtained abundant physical experiment results.These results show that the diagnosis has reached the expected design goal,and can provide related physical information such as plasma edge density fluctuations,and lay a good diagnostic foundation for the J-TEXT Tokamak edge turbulence research.