| Future tokamak discharges will be mainly operated with high parameters and high beta(the ratio of the plasma pressure to magnetic pressure).With the increase of beta,the electromagnetic turbulence grows,and its impacts on confinement and transport increase,which may even exceed the impacts of the electrostatic turbulence.Therefore,the development of the diagnostic systems measuring electromagnetic fluctuations is of great significance for future magnetic confinement fusion research.By receiving the scattering signal from plasma with a polarization direction perpendicular to the polarization direction of the incident microwave,the cross-polarization scattering diagnostic system measures the magnetic fluctuations in plasma,and is an important means for the research of electromagnetic instabilities in tokamak plasma.The main work of this thesis contains the development of cross-polarization scattering diagnostic system on EAST,and the detailed research on quasi-coherent mode in H mode discharges using Doppler microwave reflectometry and cross-polarization scattering system.In the thesis,the development of the V-band integrated system of crosspolarization scattering(CPS)and Doppler microwave reflectometry(DR)is accomplished,including the installation and testing on EAST,to achieve the simultaneous measurements of density fluctuations and magnetic fluctuations.The locations and the wavenumbers of the measured magnetic fluctuations are analyzed by ray tracing.The CPS and DR diagnostic systems share the same transmitter,and the receiving antenna of the DR and that of the CPS are separated along the toroidal direction.Under the current discharge parameters,the density fluctuations are much larger than the magnetic fluctuations,so the slight leakage of the density fluctuations signal can cover the magnetic fluctuations signal,so that the effective data of the magnetic fluctuations won’t be obtained,which is the difficulty of the design of CPS system.In EAST,the tests are completed for both X-mode(extraordinary mode)and O-mode(ordinary mode)injections.The results show that the CPS measuring data distinguishes from DR measuring density fluctuations obviously,which indicates that the CPS measuring data is not the leakage of density fluctuations,but the real magnetic fluctuations.The feasibility of CPS diagnostics on EAST is verified.Based on the development of the V-band single-channel CPS system,the construct of the E-band multi-channel integrated system of CPS and DR is completed,aiming at the improvement of the discharge parameters(higher magnetic field and density)on EAST.The integrated system can cover the whole pedestal and part of the core region,measuring the fluctuations at 6 different radial positions simultaneously,and the measuring locations can be changed flexibly according to the experimental demands.The system is based on the comb generator and frequency multipliers,launching the microwave beams covering E-band(60 GHz-90 GHz)with 1 GHz interval into plasma.The desired detecting frequencies are selected by adjusting the frequency of the reference microwave,so that the adjusting of the measured positions.The research in the thesis contains the design of the optical system,the construct of the electronic system,tests in the laboratory,and the ray tracing calculations.In the design of the optical system,the optical parameters are calculated such as the positions and focal length of the front mirrors,the positions of the corrugated circular waveguides,and the focal length of the coupling lens.The front optical system has been put into use since 2021,and it meets the expectations of the design.The output multi-channel signals are analyzed,and the function changing the detecting microwave frequencies due to the variation of the frequency of the reference microwave is tested,which has verified the feasibility of the electronic system scheme.The Doppler microwave reflectometry brunch of the E-band multi-channel system has been put into use at present,which is one of the routine tools for turbulence measurements in EAST experiments,with a large amount of experimental data obtained.The quasi-coherent mode(QCM)(3 kHz-100 kHz),which is ubiquitous in H mode discharges,has been investigated by DR and CPS diagnostic systems on EAST:this mode can exist in ELM-free H mode and Inter-ELM period widely,rotating along the electron diamagnetic direction,with a poloidal wave number ke～0.6cm-1,and is an electrostatic dominated mode.The mode rotates with plasma and the mode frequency is directly proportional to the poloidal velocity measured by DR system,and the radial distribution shows that the mode is excited near the top of the pedestal,and then propagates outward and inward at the same time.The mode can propagate as far as p～0.75 of the core.The QCM exists in the H mode discharges widely,which is irrelevant to the operation conditions such as longitudinal field of the magnetic field,density,auxiliary heating method and q95 value.The six-field two-fluid BOUT++theoretical simulation shows that the QCM belongs to drift Alfven wave instability,rotating along the electron diamagnetic direction with a poloidal wave number kθ～0.5828cm-1,and has a tendency to propagate inward,which is consistent with the experimental results.Combined with the previous simulation analysis of BOUT++,it is believed that the QCM is related to particle transport.The research on this QCM is helpful to the further understanding of the transport problem in tokamak,and will be beneficial to the long-pulse steady-state operation in EAST.A high-frequency quasicoherent mode in H mode discharges has also been observed on EAST,and the frequency of this mode is 200 kHz-300 kHz,which may be affected by electron temperature gradients in the pedestal region.It is found that the resonant magnetic perturbations can suppress this mode. |
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