Experimental Study On The Characteristics Of Broadband Electron Temperature Fluctuations In EAST

In the burning plasma,the ? particles produced by the core nuclear fusion reaction of the plasma will transfer their kinetic energy to the main ion mainly through the electrons,thereby realizing the self-sustained steady state by self-heating of a particles.Therefore,understanding the physical mechanism of the electron heat transport is essential to predicting and improving the performance of the burning plasma.The physical quantities related to the electron heat transport that can be measured experimentally mainly include:the electron heat diffusivity that describes the macroscopic characteristics of the electron heat transport,and the electron temperature/density fluctuations that characterize the microscopic nature of the electron heat transport.This master's thesis presents the characteristics of broadband electron temperature fluctuations under different plasma scenarios on EAST,with a focus on the study of the excitation con-ditions and the underlying physical mechanism of the broadband electron temperature fluctuations in the ohmic plasmas.The work in this thesis mainly contains two parts.The first part focuses on the data analysis methods of several key physical quantities in the experimental research of the electron heat transport.They are the electron temperature fluctuations,the electron temperature and density gradients.The length of time for cross-correlation analysis for calculating the electron temperature fluctuations is determined,and a more accurate value of the electron temperature fluctuations is obtained.By comparing the electron temperature profile given by different diagnostics,it is verified that the electron temperature profile measured by the ECE diagnostic is reliable.The effects of a series of parameters in the fitting process of the electron temperature profile on the results are studied.The results show that the fitting results agree with the original data best when the order of the polynomial fitting function is the third order and the average time is 10 ms.The electron temperature gradient is calculated using the fitted electron temperature profile.The electron density fitting was optimized by using the same procedure,and a better fitting result is obtained,and the electron density gradient is calculated.The second part presnts the results of the broadband electron temperature fluctuations under different plasmas parameters in EAST,including:the ohmic density ramp-up plasmas,the L-mode plasmas with different auxiliary heating,and the ELM-free H-mode plasmas.For the ohmic density ramp-up plasmas,it is found that the amplitude of the electron temperature fluctuation changes significantly during the electron density ramp-up phase.Comparing the relationship between the electron temperature fluctuations and the energy confinement time,it is found that the degradation of energy confinement is obviously related to the electron temperature fluctuations.The relationship between the electron temperature fluctuations and the electron temperature and density gradient is studied,and it is found that there is a window phenomenon where the electron temperature fluctuations is at a relatively high level.Analyzing the relationship between these three quantities,it is found that the excitation condition of this turbulence is related to both the electron temperature gradient and the electron density gradient,and its stability boundary can be approximately expressed as R/LTe=4.5 R/Lne-1.1,where R/LTe is the normalized electron temperature gradient,R/Lne is the normalized electron density gradient.The electron density fluctuations for a frequency range less than 40 kHz measured by DBS is consistent with the evolution of the electron temperature fluctuations.Linear analysis shows that the electron temperature fluctuation that the CECE diagnostic observes is attributed to the ITG turbulence.The evolution of the flow shear and the carbon impurity implies that the changes in electron temperature fluctuations observed in the electron density ramp-up plasma may be a synergy effect of flow shear,impurities,and diagnostic capabilities.In addition,the characteristics of the electron temperature fluctuations under other plasma scenarios are also analyzed.In the L-mode plasmas with different auxiliary heating,the electron temperature fluctuations show different behaviors.The results imply that the main physical quantity that determines the characteristics of the electron temperature fluctuations is the electron temperature gradient.Under the condition of ELM-free H-mode plasmas,the quasi-coherent mode is observed in the radial range of?=0.71-0.87.