H. Iguchi

K. Matsuo

K. Matsuoka

M. Kawakubo

N. Uchida

S. Kado

S. Okamura

National Institute for Fusion Science (NIFS-Repository)

§ 14. Measurements of Electron DensityFluctuations in CHS Plasmas by UsingYAG Laser Imaging MethodMatsuo, K. (Fukuoka Institute of Technology),Uchida, N. (Fukuoka Institute of Technology),Kawakubo, M. (Fukuoka Institute of Technology),Iguchi, H., Okamura, S., Matsuoka, K., Kado, S.(The University of Tokyo)shows an example of the 2D power spectra at f=29.5 kHzby the contour lines. There are some non-symmetricalpeaks on the spectrum, which predicts that the propagationdirection and position of the density fluctuations are nouniform. We plan to find the distribution of the densityfluctuation by developing this analysis.Optical FiberFig. 1 Laser Imaging System for CHS.Fig. 2 An example of power spectra S(kx,ky,t) at1.5f2=100mmPhase Mirrorn=2000mmThe maximum and minimum-.5 ° .5kx (mm A -l)-1Personal ComputerDNoise Stabilizer-1.5values of the contour lines are different by 20times. The vertical axis indicates thewavenumber ky (-1.88 "'-' 1.88mm-1) and thehorizontal axis indicates the kx(-1.88"'-'1.88mm-1).f=29.5kHz._0.9... 0.8... 0.7_0.6-1-.51.5-1.5We have applied a novel technique of a YAG laserimaging method for obtaining information on electrondensity fluctuations, including the spatial distribution inCHS plasmas. A two dimensional image of the densityfluctuations, which had not been measured until now, weremeasured in this fiscal year.Figure 1 shows the optical system for CHS. TheYAG laser O"j= 1.064 /-lm, 1.2 W) beam is transported by anSM optical fiber near the CHS plasma. A radiation beamfrom the SM fiber is expanded and collimated by a beam-expander and passes through the plasma. The probebeam is then transmitted through focusing and imaginglenses along with a phase mirror, and then received by a onedimensional 16-fiber array connected to low noise detectors.In addition to the one dimensional spatial measurementsmade last year, a two dimensional spatial measurement atthe detecting plane was performed by making the detectorarray to rotate shot by shot this fiscal year. Themeasurable frequency range determined by the frequencyresponse of the detector was 20 kHz to 1 MHz. Themeasurable wavelength range determined by the beamwidth and number of detector channels was 2 mm to 47 mm.A spatial resolution of about 20 mm at k=l mm-1 around theplasma edge was estimated.Plasma is initially produced and heated by ECH andfurther heated by NBI. The spectrum of the densityfluctuation distributes broadly between 20 kHz - 300 kHz,and decreases as frequency increases. The data from thedetector array was analyzed by the FFT to obtain the crossspectra C(x,y,f) and power spectra S(kx,ky,t). Figure 2274

Measurements of Electron Density Fluctuations in CHS Plasmas by Using YAG Laser Imaging Method

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