Multi-channel Doppler Reflectometer System And Improved Confinement Mode Investigation On EAST Tokamak

Doppler reflectometer(DR)is a safe and localized turbulence diagnosis with high temporal resolution and wavenumber resolution.It can provide the poloidal rotation,density fluctuation(turbulence)and perpendicular velocity perturbation of localized plasma.The aim of this thesis is to design,build,adjust and test a complete W-band(75-110 GHz)5-channel Doppler reflectometer including the front-end optical system,microwave-electronics system,control and acquisition system installed at Experimental Advanced Superconducting Tokamak(EAST)-G port,and to analyse the experimental data and detailed physics behind these observations.Also,a study of I-mode(a plasma operation mode with both L-mode particle confinement and H-mode energy confine-ment)on EAST has been made through the 8-channel V-band system.Except for an introduction of the research status of controllable fusion,the detailed expressions about the measurement principle of the Doppler reflectometer(DR),the component analysis of the DR signal,and various data processing methods that can be used in the DR data analysis have been made in the introduction part.We designed and installed a W-band multi-channel DR system in EAST-G port according to the experimental requirements and the diagnosis port actuality on EAST.In this thesis,the shared front-end optical path system between the new W-band system and correlation electron cyclotron emission(CECE)is described in detail.The front-end optical path is divided into two parts outside the vacuum chamber and inside the vacuum chamber,and two main long-distance microwave transmission schemes inside the vacuum chamber,waveguide stretching into the vacuum chamber and full vacuum propagation,have been described in detail and simulated.Considering the demand on optical alignment,the new system chooses the waveguide stretching into the vacuum chamber scheme with a rotatable plane mirror to adjust the microwave launching an-gle.Also the design of focusing mirror and the dielectric-slab microwave beam splitter(making the DR and CECE share the same optical path)are introduced in detail.In terms of electronic system design,a new scheme of combining an I/Q type double side-band modulator and a sextupler from the laboratory test experience is chosen as the scheme of the new WDR,and a modulation frequency of 400MHz is determined.The new multi-channel technology makes the system adjusting the most difficult part of this work.This paper introduces the detailed adjusting scheme.The YIG filter working on both the lower sideband frequency(f0-450 MHz)and the upper sideband frequency(f0+450 MHz)can acquire available multi-peaks.According to best multi-peaks and system stability,the upper sideband frequency scheme with a drive circuit frequency of 6*.f0+2.7 GHz is chosen,and multi-channel launching frequencies 6*f0++f*0.4 GHz,an effective operating frequency range of the system is 75-97.8 GHz are achieved.Ray-tracing calculations under kinds of plasma parameter have been made to figure out the radial coverange ability of the new DR system in this thesis.And the NI controlling,collection and storage kits are used in the controlling and data acquisition system of the WDR and CECE integrated diagnosis.Finally,more in-depth tests suggest an upgraded scheme from the monostatic system to transceiver separation to improve the signal-noise ratio and a new frequency extend scheme to increase the frequency coverage ability in one measurement.Then,the experimental operation of the new WDR on EAST is introduced,and some observations such as ne-Te coherent structure,tearing mode and H-mode eigen-mode GAM are studied in this thesis.Detailed joint measurement results between the WDR and CECE including a weak correlation structure between density fluctuation and electron temperature fluctuation and a strong correlation structure between radial elec-tric field perturbation and electron temperature fluctuation are described in this thesis.In the tearing magnetic island observations,a clear double-peak structure in the DR tur-bulence spectrum and many tearing mode harmonics introduced by the turbulence and shear flow spatial distribution around the island region have been observed.Also in the thesis,the observations of strong turbulence inside the magnetic island,strong flow shear at island separatrix and strong asymmetry at front and back boundaries are also described.Preliminary investigation shows that the turbulence inside magnetic island may be excited by the impurity peak inside the island.In the study of H-mode eigen-mode GAM,the mode characteristics,existing radial region,spatial structure,radial propagation and bispectrum analysis results of H-mode GAM are described in detail.Additionally,a rough statistical research of H-mode GAM has been made in this thesis.Finally,the first I-mode research on EAST with the 8-channel V-band DR has been made.The history of I-mode observation and investigation is introduced firstly,and the I-mode macro characteristics,micro disturbance and statistical research results achieved on foreign devices are summarized systematically.The I-mode study starts from the I-mode identification.We innovatively start from the I-mode plasma micro boundary fluctuations and then combine with the macro parameter characteristics.Fi-nally,the existence of I-mode on EAST device is confirmed,and the judgment standard of I-mode on EAST device is summarized.After I-mode confirmed,two I-mode char-acteristic modes LFO 5-10 kHz,WCM and the observed GAM have been investigated detailed in this thesis.Multi-diagnosis data analysis shows that the LFO is essentially a local boundary temperature ring oscillation(ETRO),and it should periodically excite strong electron diamagnetic directional(EDD)turbulence through periodic local elec-tron temperature gradient evolutions,thus forming the Er well observed at the I-mode boundary.And the strong electron direction turbulence is observed strongly coupling with the WCM through modulation,and then causes periodic radial outward particle transport in LFO-frequency observed in diverter probes leading to the enhanced par-ticle transport,a low particle confinement and the long-pulse stable operation of the I-mode.Significantly,the second harmonic frequency of LFO is first explained in the drift-wave zonal-flow system through the asymmetry of perpendicular velocity in ion direc-tion and electron direction caused by periodic turbulence excitation.Bispectral analysis shows that there are strong interactions among LFO,WCM and background turbulence,and the observed background turbulence suppression in the strongest gradient region of temperature pedestal should be from the energy transferring from background turbu-lence to LFO and WCM,improving systematic understanding of the I-mode formation.Also,in this thesis,the characteristics of heating methods,operation space,Er well depth,power threshold and energy confinement of the I-mode have been also investi-gated,and the preliminary I-mode operation experience has been obtained to guide the active controllable I-mode operation.