A modulated microwave reflectometry has been successfully developed on HL-2A, which can be used to measure the plasma density profile with time-delay method. This microwave reflectometry has two frequency ranges (26.5 to 40 GHz and 40 to 60 GHz) and it is suitable for measuring the plasma density ranging from 0.8×10^(13) cm^(-3) to 4.5×10^(13) cm^(-3). The temporal resolution is 1 ms and the spatial resolution is about 1 cm. This paper will present the basic principle of the microwave reflectometry, parameters calibration of the equipment and the experimental results on HL-2A tokamak.
DING Xuantong YANG Qingwei YAN Longwen LIU Dequan XIAO Zhenggui ZHU Genliang LIU Yi ZHOU Yan PAN Yudong CUI Zhengying LIU Zetian SHI Zhongbing JI Xiaoquan XIAO Weiwen LIU Yong
The fluctuation of the electron temperature has been measured by using the electron cyclotron emission imaging in the Hefei Tokamak-7(HT-7) plasma.The electron temperature fluctuation with a broadband spectrum shows that it propagates in the electron diamagnetic drift direction,and the mean poloidal wave-number kθ is calculated to be about 1.58 cm-1,or kθρs≈ 0.34.It indicates that the fluctuation should come from the electron drift wave turbulence.The linear global scaling of the electron temperature fluctuation with the gradient of electron temperature is consistent with the mixing length scale qualitatively.Evolution of spectrum of the fluctuation during the sawtooth oscillation phases is investigated,and the fluctuation is found to increase with the gradient of electron temperature increasing during most phases of the sawtooth oscillation.The results indicate that the electron temperature gradient is probably the driver of the fluctuation enhancement.The steady heat flux driven by electron temperature fluctuation is estimated and compared with the results from power balance estimation.
The pulse propagations of both the electron temperature and the electron densityhave been observed during pulse-modulated molecular beam injection experiments on HL-2A.Thepropagation depth of the cold pulse in the low field side is much longer than that in the high fieldside.The cold pulses cannot propagate to the plasma center from either the low field side or thehigh field side.The electron temperature in the plasma center does not change during MBI,butthe electron density pulse perturbations can be observed in the plasma center.
Drift instability in plasma generated by electron cyclotron resonance (ECR) in KT-5D device was investigated by using a fast camera and Langmuir probes.The similarity betweenthe distribution of light intensity from the images and the plasma pressure indicates a nearly linearrelationship.The discharge images taken by the camera and the plasma parameters measured bythe probes also indicate the existence of low frequency turbulent events with a time scale less thana few mini-seconds.
An upgraded electron cyclotron emission imaging (ECEI) system consisting of newoptics lenses with necessary electronics for receiving and processing signals for two dimension(2D) ECEI diagnostics was installed on EAST. Hyperboloid lens were adopted in the new systemto optimize the spatial resolutions. The mixers array of sixteen elements measured the plasmaelectron cyclotron emission at eight frequencies simultaneously, and the profiles of the electrontemperature and its fluctuation in an area of 20 cm (vertical) × 6 cm (horizontal) could then beanalyzed. Evolution of sawtooth precursor and crash in EAST was observed.
Based on the single biasing electrode experiments to optimize the confinement ofplasma in the device of KT-5C tokamak,dual-biasing electrodes were inserted into the KT5Cplasma for the first time to explore the enhancing effects of biasing and the mechanisms of thebiasing.By means of applying different combinations of biasing voltages onto the dual electrodes,the changes of E_r,which are the key factor for boosting up the E_r×B flow shear,were observed.The time evolution showed that the inner electrode played a major role in dual-biasing,whichdrew larger current than the outer one.The outer electrode produced little influence.It turnedout that the dual-biasing electrodes were as effective as a single one in improving the plasmaconfinement,for the mechanism of biasing was essentially an edge effect.
Spatio-temporal evolutions of the sawteeth activities are measured simultaneously with a 16 channel high spatio-temporal resolution electron cyclotron emission(ECE)heterodyne radiometer on HT-7 and the evolutions of the sawteeth are found to be diffusive in character. By a perturbative analysis,the electron heat diffusivity χ_e inferred by time-to-peak method and Fourier transform shows a good agreement.The value of electron heat diffusivity shows radial asymmetry between the low magnetic field side(LFS)and the high magnetic field side(HFS).It is observed that with the increase in plasma density,the electron heat diffusivity decreases and the confinement of energy is improved.By comparing with χ_e^(pb)inferred by static power balance analysis,the result indicate that χ_e^(hp)is larger than XpD by a factor ranging from 2 to 10.
