22P115-P
Accuracy improvement of ablated plasma measurement with Thomson
scattering measurement method
トムソン散乱計測法を導入したアブレーションプラズマ計測の精度向上
K.Nishimura, T.Ohishi, T.Kono, S.Misaki, N.Ohmoto, T.Yabuuchi, K.A.Tanaka
西村清秀, 大石達也, 河野卓也, 御前成吾, 大本直輝, 薮内俊毅, 田中和夫
Graduate School of Engineerig, Osaka University , Yamada-oka 2-1, Suita, Osaka 565-0871 Japan
大阪大学大学院工学研究科 〒565-0871 大阪府吹田市山田丘 2-1
Two laser ablated carbon plasmas are crossed each other and formed a plasma column at the intersection in
our laser experimental platform. At the intersection carbon product materials such as Onion fullerene,
CNT and CMT etc. are created, but their forming conditions are not understood well. As a mean to obtainthe conditions and to study the forming details, the intersection was irradiated at Nd:YAG laser (2ω, 8ns,10Hz) as a basic step toward the Thomson scattering. Using a 30 nsec (time frame) 2D image camera, we
could catch the scattering from these carbon materials clearly.

1. Introduction
In the study of plasma ablation assumed in IFE
chamber wall, it is possible to promote detailed
understanding the plasma by conducting asimulation experiment using pulse laser beams. In
our experimental platform, the ablated plasma
electron temperature and density are measured byLangmuir probes. This diagnostic method may
encounter difficulty to measure the characteristics
of high temperature and density plasmas in the case.
Then as alternative plasma diagnostic method, wewill employ Thomson scattering (TS) technique.
This method is contactless with the plasma and highspatial resolution is porssible. We started thepreparation for the TS measurement by irradiating
the ablated carbon plasma (Te ~6eV, Ne ~1019/cm3)
with Nd:YAG laser (2ω, 8ns, 10Hz). Even at thispreparation phase we observed very interesting
features only possible from our experimental
platform. The intersection of two laser ablated
carbon plasma, where a plasma column is formed
and carbon product materials including Onion
fullerene, CNT and CMT are created [1]. This
plasma column is irradiated at Nd:YAG laser (2ω,8ns, 10Hz) and the scattered emission are measured.
We have observed emission not directly from theplasma scattering, but very possibly from these
CNT and CMT particles. Since their forming
conditions are not understood well, this method canbe a useful tool to understand the formation ofmaterials such as Onion fullerene, CNT and CMT.
2. Experimental setup
Figure 1 shows a schematic diagram of theexperimental setup. To measure scattered light fromcarbon product materials, a plasma column isformed using the experimental setup "LEAF-CAP"(Laboratory Experiments on Aerosol Formation byColliding Ablation Plumes) [2]. Nd:YAG laser (3ω,6ns, 10Hz) is optically split into equal-power. Each
split beam is line-focused (~0.1mm by ~1cm,10~11J/cm2/pulse) to radiate two cone cave targets(Carbon) at room temperature in a vacuum chamber(~10-6torr). The ablated plasma plumes are crossed
each other at 12.8 mm away from the target
surfaces and formed a plasma column (Te ~1eV, Ne~1012/cm3). Nd:YAG laser (2ω, 8ns, 10Hz, φ~8mm) can be injected at any desired timing and canlead to scattering if there are any scattering sourcesat the intersection. Scattered emissions are observed
at a specific time with an intensified CCD (ICCD)
camera. A 2 ω band pass filter (524~532nm,42~61%) has been used in front of the camera due
to measure the scattered emission since the plasma
emission coming from the intersection includes
broad wavelength spectrum and the Carbon Swanband [3]. ICCD camera can measure 2D frame
photo with 30 nsec time window with a variable
time delay.
3ωNd:YAG Laser
Vacuum Chamber
3ωNd:YAG Laser

ICCD measuringrange

Cone cave target(Carbon)
Figure 1 A schematic diagram of the experimental
setup2ωNd:YAG Laser

3. Result and Discussion
Figure 2 shows an image how the laser ablated
carbon plasmas cross each other, collide andstagnate. We know that there are many carbon
product materials created through this process in theexperiment. Figure 3 shows the result of ICCD
observation (30 nsec time framed 2D image). The
observation field of view corresponds to the redcircles in Figure 1 and Figure 2 when plasma
emission is the most strong in a sequence of ablated
carbon plasma.
When 2ωNd:YAG laser crossed plasma column,
the scattered emission was measured around theplasma column repeatedly. The image was taken
through the 2ω band path optical filter. The straylight was carefully removed from the measurement.
As a result of comparing the result of Figure 3 with
2ωNd:YAG laser only or 3ωNd:YAG laser ablated
plasma only, the emission in Figure 3 is thescattered emission from possibly the carbon productmaterials generated between inducing two ablated
plasma plumes and crossing each other.
Cone cave target (Carbon)

Scattered emission

2ωNd:YAG Laser~8 mm

12.8mmAl tape

Plasma emission

Cone cave target(Carbon)
Figure 3 ICCD observation at the timing ofmax emission from the plasma column. The
scattered emission indicates the scatteringfrom carbon products.

Acknowledgments
We are indebted to Prof. Yoshi Hirooka, NationalInstitute for Fusion Science, Toki Japan and Dr
Atsushi Sunahara, Institute for Laser Technology,
Osaka Japan, Prof Ahmed Hassaneing, Purdue
University, U.S.A. for the fruitful discussions.

Electron temperature [eV]

References

0

1 Distance[cm]emission
Figure 2 Ambience of laser
ablated carbon
plasma and carbon product materials

4. SummaryIn the intersection where two carbon plasma
plumes crossed each other, it is known to createcarbon product materials. In the 30 nsec 2D imaged
ICCD photo, we have captured clearly the scatteredemission from possibly the carbon cluster formation.
The formation may include CNT, CMT and Onion
fullerene etc. The level of scattered light from boththese product and plasma columns can be used toevaluate the laser intensity necessary for Thomson
scattering measurement. We have shown that the2 probe laser can be used to study the amount andkinds of their materials using.

[1] Y. Hirooka, T. Ohishi, K.A. Tanaka presented as
T3-OS-14/3085 at 19th Topical meeting on theTechnology of Fusion Energy, Nov 7-11 2010, Las Vegas
and submitted to FS & T.
[2] Y. Hirooka, T. Oishi, H. Sato and K.A. Tanaka,Fusion Science and Technology. 60(2011).
[3] Y. Hirooka, K.A. Tanaka, H. Sato, K. Ishihara and A.
Sunahara, J. Phys., 244 (2010)[4] 分光技術ハンドブック(朝倉書店 1990)