25aE20P
直線プラズマのトモグラフィ計測とウェーブレットによる揺動の時空間発展解析	 	 Tomography measurement and wavelet analysisof spatiotemporal dynamics of fluctuations in a linear plasma
福永史樹1, 藤澤彰英2,3, 永島芳彦2,3, 柴田遼介1, 濱本直紀1, 江藤健太1, 稲垣滋2,3 , 糟谷直宏2,3, 山田琢磨3,4,
小菅祐輔5, 佐々木真2,3, 伊藤早苗2,3, 伊藤公孝3,61
Fumiki Fukunaga , Akihide Fujisawa2,3, Yoshihiko Nagashima2,3, Ryousuke Shibata1, Naoki Hamamoto1 et al.
九大総理工1, 九大応力研2, 九大極限プラズマ研究連携セ3, 九大基幹教育院4, 九大高等研究院5, 核融合研6
IGSES Kyushu Univ.1, RIAM Kyushu Univ.2, RCPT Kyushu Univ.3, FAS Kyushu Univ.4,
IAS Kyushu Univ.5, NIFS6
Effect of plasma turbulence on plasma confinement should
be studied in order to produce high performance plasma forthe realization of nuclear fusion reactor. The turbulence iscomposed of the fluctuations of various spatiotemporalscales therefore; it is necessary to observe plasma turbulence
not only at the local region but also over the entire plasma.
Tomography is one of the methods that satisfy therequirement. 	  For measuring plasma turbulence,
tomography is being developed in Plasma Assembly for
Nonlinear Turbulence Analysis (PANTA)[1]. In thetomography system, the first results of the spatial evolutionof the local emission profile are obtained in every 1 µs withparallel computing of 120 cores.
The tomographyreconstruction with such high temporal resolution allows us
to evaluate not only Fourier spectral analysis but also
temporal evolution of local fluctuation spectra using wavelet
analysis.
In PANTA, cylindrical argon plasma is produced from thehelicon antenna with the diameter of 0.1 m. The
experimental results introduced here are obtained in Arplasma under the condition that magnetic field is 900 G andgas pressure is 1 mTorr, The tomography system has four
detector arrays set on different azimuthal positions every 45°
degrees apart. The measurements are performed for ArI andArII emissions; blue (476.5 ± 20 nm ArⅡ), and infrared(900 ± 25 nm ArⅠ) light. Tomography images of the local
emission profile are reconstructed using the Maximum
Likelihood-Expectation Maximization (ML-EM) technique.	 
The ML-EM is one of the tomography algorithms to deduce
local values through iterative calculation from a set ofline-integrated signals.
Figure 1(a) shows an example of the local emission profileof ArII. The local emissions are calculated as values on 121(= 11 x 11) grids with width of ~ 14.5 mm on theobservation square (160 mm x 160 mm). Such tomographic

images and local emissions are obtained in every 1 µs.
Figure 1(b) shows temporal evolution of local emission
intensity at the plasma center denoted position A (x = 0, y =0 mm) with that of position B (x = - 15, y = - 15 mm).
Figure 1 (c) shows the Fast Fourier Transform (FFT) power
spectra at position A and B with frequency resolution of Δf =0.122 kHz in the period from 0.10 ms to 0.58 ms.
Since the temporal evolution of local emission is calculated
in such a high resolution of 1 µs, the fluctuation power canbe evaluated up to the Nyquist frequency of 500 kHz.
Utilizing the high temporal resolution, we can deduce atemporal evolution of frequency spectra using wavelet
technique. The definition of the wavelet analysis is!
𝜔! (𝑓, 𝑡)    = !! 𝜀  ( 𝜏)  𝛷  (𝑓, 𝑡 − 𝜏)  𝑑𝑡with 𝛷  (𝑓, 𝑡 − 𝜏) =    𝑓𝑒𝑥𝑝  [𝑖2𝜋𝑓𝑡 − (𝑓𝑡)! /2] [2].
Figure 2 shows the result of wavelet analysis at position C (x= 0, y = 15 mm) from 0.10 s to 0.58 s, where the ArIemission has a maximum, with the temporally averaged
power of the wavelet spectra. The wavelet analysis clearly
demonstrates the presence of temporal variation in thecoherent mode around 2.5 kHz, and rather turbulent activity
around 4 kHz.
In summary, temporal evolution of local emission over theentire plasma is successfully obtained in every 1 µs with thetomography system using MLEM algorithm on cylindricallinear plasma, PANTA. The high temporal resolution
enables us to analyze properties of local fluctuations, notonly with Fourier spectra but also wavelet spectra. As future
work, spatial correlations between local emissions and thosebetween their envelopes are studied with FFT and wavelet
analyses. In this poster will show the first results of local
emissions obtained with tomography, and their fluctuation
properties analyzed with FFT and wavelet analyses.

Fig.2 (a) The wavelet spectra at position C (x = 0, y = 15 mm).
(b) temporally averaged power of the wavelet spectra.
Fig.1 (a) A moment tomography imageof emission intensity of ArII at 400 ms;
900G, 1mTorr, position A (red) is
plasma center position (x = 0, y = 0mm), position B is x = -15, y = -15 mm.
(b) Time evolution result of emission
intensity at A (red) and B (blue). (c) FFTspectra at A (red) and B (blue).

References[1] S. Oldenbürger, et al., Plasma Phys. Control. Fusion
54 (2012) 055002.
[2] B. Ph. van Milligen, et al., Review of ScientificInstruments 68, 967 (1997)