23P047-P
Measurement of ion temperatures in plasma blobs
by using statistical analysis methods
統計的解析手法を用いたPlasma Blob中のイオン温度計測
Katsuya Okazaki1, Hirohiko Tanaka2, Noriyasu Ohno1, Naomichi Ezumi3,Yoshiyuki Tsuji1 and Shin Kajita1
1
岡崎克哉 , 田中宏彦2，大野哲靖1，江角直道3，辻 義之1，梶田 信1
1

Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
2
NIFS, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan
3
Nagano National College of Technology, 716 Tokuma, Nagano, Nagano 381-8550, Japan1
名古屋大学 〒464-0075 名古屋市千種区不老町
2
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
3
長野工業高等専門学校 〒381-8550 長野県長野市徳間716
Heat load caused by plasma blobs is thought to be attributed by the energy of ions. Thus, measurement ofion temperature in plasma blobs is important. In this research, we measured the ion and electron
temperatures in plasma blobs observed in a linear plasma device by using an improved ion sensitive probe
and statistical analysis methods. As a result, it was found that ion and electron temperatures in the plasma
blobs decrease more slowly than those outside of plasma blobs in the radial direction

1. Introduction
Intermittent convective plasma transport infusion edge region called a blobby plasma transport
is thought to be one of the most importantphenomenon. The plasma blob propagates toward
the cross-field direction in scrape-off layer oftokamak devices. The blobby plasma transport isthought to enhance particle and heat fluxes onto afirst wall and total kinetic energy of plasma blobs
near the wall could be mainly determined by ion
temperature (Ti). Therefore, the ion temperature inplasma blobs is necessary to estimate theconvective heat transport by the plasma blobs.
The blobby plasma transport has been widelyinvestigated at not only tokamaks but also linear
and helical devices. In this study we will investigate
radial distribution of ion temperature to investigate
how the cross-field transport could affect thetemperature distribution by using an ion sensitive
probe (ISP) and statistical analysis methods in thelinear divertor plasma simulator NAGDIS-II [1].
2. Experimental Setup
In order to measure the Ti in plasma blobs, an ISP[2,3] that was combined with a single Langmuirprobe (LP) was newly developed, as shown in Fig.
1. In addition, it is necessary for precise
measurement of the Ti to reduce noise components
in high-frequency domain as much as possible,
because the blobby plasma transport is a high-speed
phenomenon. Therefore, we have reduced noiselevel by an improvement of measurement system,

Fig.1. Improved measurement system and structureof the new probe head composed of ISP and single LP.

as described in Fig.1. In this circuit, two electrodesof the ISP were isolated by using two bipolar power
supplies and two wave generators. Moreover,length of transmission cables between theelectrodes and the digitizer were set as short aspossible.
3. Analysis Procedure
Figure 2 shows a diagrammatic illustration of
the analysis procedure. A positive spike in ion
saturation current (Isat) was observed when a plasma
blob passed across the LP because the fluctuation ofIsat is mainly proportional to that of plasma density.
Thus, we can detect the times when plasma blobs
passed and didn't pass through the LP by setting aproper threshold value for the Isat fluctuation.
Before detecting the positive spikes in the Isat,
numerical low-pass filter based on fast Fourierrespectively. It was found that the decay rate withplasma blobs tends to be smaller than that outsideof the plasma blobs. This result suggests that theTi gradient would become loose due to the plasma
blobs.

Fig.2. Outline of analysis procedure.

transform was applied to the Isat signal in order toobtain the filtered Isatf, because the high frequency
noise in Isat attributes a false detection of thepositive spikes which correspond to the plasma
blobs.
In the next step, ion current (Ip) and voltage (Vp) at
the detected times were extracted, where the Ip andVp were measured by the inner electrode of the ISP.
Because there was finite internal distance between
the electrodes of the ISP and the LP, we took thetime delay of those signals into account. Finally, wereconstructed Ip-Vp characteristics inside andoutside of the plasma blobs, and then, we calculated
Ti of them.
4. Experimental Result
The Isat and Ip fluctuations were measured
simultaneously at positions ranging from r = 10 mm(edge of the plasma column) to 30 mm every 2 mmin the radial direction.
Reconstructed Ip-Vp characteristics with andwithout plasma blobs at r = 24 mm are shown inFig. 3(a). Figure 3(b) shows the radial distributionsof Ti evaluated from the reconstructed Ip-Vpcharacteristics. Additionally Ti obtained by theconventional method with all signal is plotted. Itwas found that Ti in the plasma blobs is higher thanthat outside the plasma blobs. This result suggeststhat the thermal load was increased by existence ofthe plasma blobs at the plasma periphery .
Next, we evaluated decay rates of the Ti
distributions. The decay rate was defined as thefollowing equation:

decay rate ≡T −T∆T= − r = 20 r =10 .
∆r
20 − 10(1)The decay rates of the ion temperatures with andwithout the plasma blobs are 0.048 and 0.074,

Fig. 3(a) Reconstructed Ip-Vp characteristics at r = 24mm and (b) radial distribution of the ion temperatureswith (circle) and without plasma blobs (cross).

5. Summary
We developed an ion sensitive probe
measurement to measure the ion temperature insideand outside of the plasma blobs observed in thelinear plasma device. As a result, it was confirmedthat ion temperature increase by the coming ofplasma blobs, qualitatively. Furthermore, it should
be noted that the decay rate of the ion temperature
in a radial direction became gradual.
Acknowledgments
This research was supported by NIFS/NINS
under the project of Formation of International
Network for Scientific Collaborations. This work isalso performed with the support and under theauspices of the NIFS Collaboration Research
program (NIFS10KLPF003).
References[1] N. Ohno, D. Nishijima, S. Takamura, Y. Uesugi, M.
Motoyama, N. Hattori H. Arakawa, N. Ezumi, S.
Krasheninnikov, A. Pigarov, and U. Wenzel: Nucl.
Fusion 41 (2001) 1055.
[2] I. Katsumata: Contrib. Plasma Phys. 36 (1996) 73.
[3] K. Uehara, A. Tsusima, H. Amemiya, and JFT-2M
Group: J. Phys. Soc. Jpn. 66 (1997) 921.