Experimental Study Of Electron Temperature Fluctuations Via Correlation Electron Cyclotron Emission Radiometer System

In recent years,the anomalous transport as a kind of influence on plasma confinement performance has received extensive attention in the field of controlled nuclear fusion.Studies have shown that the anomalous transport is related to various fluctuations such as magnetic fluctuations,temperature fluctuations and density fluctuations of plasma.In order to study the anomalous transport,the correlation electron cyclotron emission(CECE)diagnostic has been proposed to measure the electron temperature fluctuations.As early as 2014,J-TEXT had developed a CECE system with four channels to observe the electron temperature fluctuations.For the observation of more physical phenomena,the CECE on J-TEXT now has been upgraded to a system with fourteen channels.First,this article introduces the improvements and upgrades of the J-TEXT CECE diagnosis.On the one hand,a series of modifications were made to the original system,including background noise improvement,hardware connection improvement and wire optimization.After the transformation,the background noise of the system drops to a level of about 30 mV,and the probability of a system failure is greatly reduced.On the other hand,some upgrades have been made for the system,including increase in channels,system flexibility improvement and system stability enhancement.After the upgrade,the system has a total of 14 channels;the flexibility of the system is greatly improved by designing the YIG band pass filter controller and digital video amplifier circuit;the steady state performance of microwave components affected by temperature is guaranteed through the design of the temperature closed-loop control system.Then,the data processing methods are introduced from the time domain and the frequency domain in combination with specific examples.The time domain analysis method is correlation analysis.On the one hand,CECE can obtain electron temperature fluctuations through correlation analysis,on the other hand,the radial correlation length of temperature fluctuations can be obtained.The frequency domain analysis methods are mainly spectrum,power spectrum density.The spectrum analysis can obtain the frequency information in the signal;the power spectrum density can help understanding the spectral distribution of the electron temperature fluctuations.Finally,the experimental explorations are carried out from two aspects based on CECE system.On the one hand,the relationship between electron temperature fluctuations and macroscopic parameters in the plasma is studied.It is found that the electron temperature fluctuations near the edge of the plasma are higher than that near the core.Further analysis results show that the density gradient has a greater influence on electron temperature fluctuations.On the other hand,the interaction between electron temperature fluctuations and magnetic islands is explored.It is found that the electron temperature fluctuations can be modulated by the rotating magnetic island,and the rotating frequency of the magnetic island changes,the modulation frequency of the magnetic island to the electron temperature fluctuations also follows.Meanwhile,it is found that the electron temperature fluctuations near the X point are higher than that near the O point.Through the analysis of the temperature profile,it is shown that the influence of the magnetic island on the temperature profile changes the temperature gradient,and the temperature fluctuations in the place where the temperature gradient becomes larger are also increased.