23P038-P
Study of filament features of edge plasma fluctuations using fast video cameras
with a combination of Langmuir probe measurements in Heliotron J (I)
L.Zang1, M. Takeuchi2, N. Nishino3, T. Mizuuchi4, S. Ohshima5, K. Kasajima6, M.Sha1, K. Mukai1,
H.Y. Lee1, K. Nagasaki4, H. Okada4, T. Minami4, S. Kobayashi4, S. Yamamoto4, S. Konoshima4,
K. Hanatani4, Y. Nakamura1, F.Sano4

臧 臨閣1， 竹内正樹2，西野信博3，水内亨4，大島慎介5，笠嶋慶純6，沙 夢雨1， 向井清史1，李炫庸1，長崎百伸4，岡田浩之4，南貴司4，小林進二4，山本聡4，木島滋4，花谷清4，中村祐司1，佐野史道4
1

Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Japan
2
Naka Fusion Institute, Japanese Atomic Energy Agency, Naka, Japan
3
Graduate School of Engineering, Hiroshima University, Higashi-hiroshima, Japan
4
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan
5
Pioneering Research Unit for Next Generation, Gokasho, Uji, Japan
6
Department of Engineering, Kyoto University, Kyoto, Japan京都大学エネルギー理工学研究所〒611-0011 宇治市五ヶ庄
In order to extract the fluctuation component from the raw data of fast camera, a pre-processing technique,Sliding Time Window Averaging Subtraction (STWAS) has been developed to remove the background ofslowly varying bulk plasma emission. Processed image shows clear filament structures. Preliminary
quantitative features of the filaments are discussed. Automatic procedure for evaluating mode number andwidth of the filament is planned.

1. Introduction
Blob is known as an intermittent turbulence
structure in the plasma edge. It is stretched along
the magnetic field line and forms k // / k   1
filament structure with much higher density thanthe background plasma [1]. Although Langmuirprobes are routinely applied to measure thepoloidal and radial structures, a fast camera canprovide 2D images of such fluctuation structuresby measuring mainly the visible light emission
from edge plasma. It features non-invasive
observation, wide view region and high spatialresolution.
It is difficult to recognize filaments in a raw
image. Phase analysis clearly shows some narrowbelts with the same phase shift, which implies theexistence of filaments [2]. However, more filament
information such as mode number and width isneeded to further understand edge turbulence. Until
now, a pre-processing method has been developed
to extract the fluctuation component from the raw
data before further analysis.
2. Diagnostics setup
In 2010, two fast cameras were installed on
Heliotron J to simultaneously measure fluctuationsin the tangential (#10.5), top and horizontal views(#11.5, Fig.1). Supersonic Molecular Beam

Injection (SMBI) is employed at #11.5 port toenhance local emission by increasing the neutral
particle density. A Langmuir probe array wasinstalled below this port, which can be used tolocate the field of view. Using the frame frequencyof 30 kHz and shutter speed of 100 kHz, filaments
were tracked in toroidal and poloidal directions
from the top and horizontal views.

Fig.1. #11.5 Fast Camera System on Heliotron J

3. Data Analysis
3.1 Pre-processing
The raw signal of fast camera data contains both
long time scale component from the slowly varying
bulk plasma "background" and short time scale
fluctuation from probably edge turbulence [3].
Fluctuation component is rather weak compared tothe "background". In this section we will focus on atypical shot in SMBI experiment with co-NBI
heating for pre-processing.
Using time average in a specified time windowaround a time point as “background” value andsliding the window point by point, we can get abackground curve Ibg. Then applying the following
equation:
If= Iraw-Ibg
where If is the fluctuation intensity, and Iraw is theraw signal, the fluctuation component is calculated.
The result with a 0.5ms sliding time window isshown in Fig.2. The extracted fluctuation is very
similar to that from a 2kHz high pass FFT filter,and we do not need to modify the distorted edge
amplitude for STWAS method. Effect of theSTWAS pre-processing is illustrated in Fig.3.
Filament structures along magnetic field line areclearly shown.

the full width half maximum (FWHM) is about 5, 8,
12 pixel, responding to actual poloidal width of
7.5mm, 12mm and 18mm, respectively. Further
work is still needed to automatically calculate theaveraged filament number/poloidal length and
FWHM in the future.

aFig.4. Fluctuation signal along a poloidal direction line at
specified time point (black) and standard deviation
during studied period (blue)b

Fig.2. 0.5ms STWAS result: a. extracted fluctuation with
2kHz high pass FFT filter (red) and STWAS (black); b.
raw signal (black) and "background" by STWAS (blue)abc

Fig.3. a. a raw image; b. an extracted fluctuation image;c. a background image

3.2 Filament tracking
After pre-processing, raw images are filteredwith respect to an amplitude and size threshold to
extract "official" filaments [4], which is defined bya critical size and amplitude conditions of thefluctuation data. Amplitude condition for each pointis set to 1σ, where σ(x, y) is the standard
deviation(STD) of time series fluctuation at point (x,y) during pre-processed regime. Size condition isset to 4 pixel at the poloidal direction, which isabout 6mm actually. However, both the twoconditions still need optimization based on more
analysis results. Figure 4 shows an example of thefluctuation signal along a poloidal direction line at
specified time point. There are three filaments andAcknowledgments
The authors are grateful to the Heliotron Jtechnical staff for conducting the experiments.
This work was performed with the support andunder the auspices of the NIFS Collaborative
Research Program.
References[1] O. Grulke, J. L. Terry, B. Labombard, et al., Phys.
Plasmas, 13(1), 012306(2006).
[2] N. Nishino et al., 20th International Toki Conference,
2010.
[3] B.D.Dudson et al., Plasma Phys. Control. Fusion
50,124012(2008).
[4] T. Windisch, O. Grulke, S.J. Zweben and R.J.
Maqueda, PPPL Reports, 4371, (2008).