Optimization Of The POlarimeter-INTerferometer Diagnostics System On EAST

The electron density profile and plasma current distribution data are fundamental parameters of the tokamak plasma.Measurement of the plasma current distribution is critical for studying plasma current transport mechanisms,understanding plasma MHD instabilities and further improving plasma confinement performance.Electron density is a basic physical parameter of plasma,and its accurate measurement is very important for the study of plasma electron density behavior and other related physical issues.Especially in the plasma disruption situation caused by proximity to the Greenwald density limit,which will threaten the safety operation of the tokamak.Therefore,real-time electron density feedback control through the plasma control system(PCS)can avoid the danger to the tokamak due to the high plasma density.The polarimeter-interferometer diagnostics system can provide electron density profile and plasma current distribution data simultaneously for physics research through interference and polarization techniques,respectively.After years of development,the measurement accuracy and the operation stability of the system have been improved significantly.The POlarimeter-INTerferometer(POINT)diagnostics system was established in 2014 aiming to explore the advanced plasma operation scenarios in EAST tokamak,to study the mechanism of current transport under different heating conditions and different wall conditions,and to study the effect of current distribution optimization on plasma confinement.And in 2015 experiment campaign,the system was successfully upgraded from 5-chord to 11-chord measurement.The work about optimization and upgrading for the POINT system has been ongoing and has kept achieving positive results,making it a key diagnostics system in EAST.The measurements of the POINT system have already been used for real-time electron density feedback control,and for the studying of current density distribution optimization and control.The topic of this thesis is mainly about optimization and upgrading of the POINT system,and performing related physics research by the POINT measurements.Firstly,the measurement principle and the components of the POINT system are demonstrated.Secondly,based on the physics model of the stray light effect,the measurement error of the Faraday rotation angle introduced by the stray light occurring on the optical path of the system is analyzed.The principle and shortcoming of the two methods for reducing stray light error are briefly described.Through the comprehensive optimization works such as polarization,collinearity,stray light and standing wave of the POINT system,the measurement accuracy of Faraday rotation angle is greatly improved,and the standing wave error is reduced from 3°-5° to 0.5°-1°.Thirdly,a system measurement error and the corresponding correction method caused by the digital phase demodulator(DPD)is demonstrated.The DPD of the POINT system can realize real-time output of the line-integrated electron density and Faraday rotation angle.The plasma refractive index could change dramatically in high electron density discharge,as a consequence,fringe jump of the line-integrated electron density may occur due to the miscalculation of DPD,which highly reduces the accuracy and reliability of the line-integrated electron density output.A program to correct the electron density fringe jump data for the POINT system is developed by analyzing and summarizing the law of the electron density jump signal,which laid the foundation for more accurate real-time electron density feedback control and calculation of plasma current distribution.Fourthly,based on the optimization of the POINT system and the accurate calculation of the electron density,the accurate and reliable plasma current distribution can be obtained by the combination of POINT measurements and EFIT reconstruction code.Electron cyclotron wave(ECW)can be used to heat electron and drive plasma noninductive current efficiently,and it is also a powerful way to optimize and control plasma current distribution.At the end of this thesis,preliminary research about the effect of different deposition location of ECRH on the plasma current distribution is performed,which provides a meaningful reference for the optimization and control of current distribution by using ECRH in the future.