24P162-B
Target material dependence of collisionless shock wave incounter-streaming plasmas
対向プラズマ中における無衝突衝撃波のターゲット材質依存性
T. Ide1 , Y. Sakawa2 , Y. Kuramitsu2 , T. Morita2 , K. Nishio3 et al.
井出尭夫 1 , 坂和洋一 2 , 蔵満康浩 2 , 森田太智 2 , 西尾健斗 3 , 桒田三沙 3 , 井手張良 3 , 坪内邦男 1 ,丹治浩樹 1 , 乗松孝好 2 , 富田健太郎 4 , 中山和貴 4 , 井上和哉 4 , 内野喜一郎 4 ,C. Gregory5 , 中堤基彰 5 , 中堤晴美 5 , A. Pelka5 , A. Diziere5 ,M. Koenig5 , S. Wang7 , Q. Dong7 , 高部英明 21Graduate School of Engineering, Osaka University 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学大学院工学研究科 大阪府吹田市山田丘 2-1
2
Institute of Laser Engineering, Osaka University2-6, Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学レーザーエネルギー学研究センター 565-0871 大阪府吹田市山田丘 2-6
3Graduate School of Science, Osaka University 1-1, Machikaneyama, Toyonaka, Osaka 560-0043, Japan
大阪大学大学院理学研究科 大阪府豊中市待兼山 1-1
4Interdisciplinary Graduate School of Engineering Sciences Kyushu University 6-1, Kasugakoen, Kasuga,Fukuoka 816-8580, Japan
九州大学総合理工学府 816-8580 福岡県春日市春日公園 6-1
5LULI, École Polytechnique, Route de Saclay, 91128 Palaiseau Cedex, France
6Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
Collisionless shock wave generation in counter-streaming plasmas for several target materials (Al,C, Cu, and Pb) is investigated using a high-power laser system. Counter-streaming plasmas areproduced by irradiating double-plane targets. As a result of interaction of the plasmas, collisionlessshock waves are observed using C, Al, and Pb in self-emission measurements. Mean-free-paths ofheavier materials become longer because the ionization degrees of each material are not much diﬀerent.

1Introduction

The laboratory simulation of astrophysical phenomenon has been tried to perform for manyyears. Physics of cosmic ray acceleration is one of
the unsolved problems in astrophysics, and collisionless shock waves are one of the most important
subjects. Y. Kuramitsu et al. [1] and T. Morita
et al. [2] have reported the collisionless shock formation in counter-streaming plasmas produced byhigh-power laser systems using double-plane targets made of CH. In this presentation, we reporttarget material dependence of shock wave generation using targets made of diﬀerent materials (C,Al, Cu, and Pb) with diﬀerent atomic mass [3].
2Experiment

The experiment was performed with Gekko XIIHIPER laser system at Institute of Laser Engineering, Osaka University. There were nine main
beams in which the energy was about 120 J/beamin 351 nm (3ω) and pulse length was 500 ps. Thetarget we used in this experiment was doubleplane target as shown in Fig. 2. In this experiment we used C, Al, Cu and Pb targets. Weput two planes parallel, and the material of twoplanes of each target was identical. The dimensions of the planes were 3 mm × 3 mm and 200 µm
thick, and the distance between two planes was4.5 mm. One of the nine beams was focused on
the inner surface of the 1st plane with 300 µm indiameter (intensity : 3.4 × 1014 W/cm2 ), and ablation plasma was formed from the 1st plane. Almost at the same time, a plasma from the 2nd
plane was created by radiation from the ablation
plasma and the ablation plasma itself. In thisway, counter-streaming plasmas were generated,and shock waves were formed by an interaction ofthese plasmas. Figure 2 shows schematic of theexperiment setup. The interaction of plasmas wasdiagnosed with a probe laser and with the selfemission. With the probe laser we obtained twodimensional information of density by shadowgraphy with intensiﬁed charge coupled device (ICCD)
cameras (200 ps gate width) and Nomarski inter-Figure 1: Schematic view of the target design.
The main laser beam is focused on the 1st plane.
Figure 3: Two-dimensional images of self-emission
Two planes are made of the same material.
taken at 15 ∼ 25 ns from the laser timing. The 1stplane is on the right side.
Fig. 3, counter-streaming plasmas are formed anddiscontinuous structures of self-emission marked
with red ovals in Fig. 3 appear as a result of interaction of the two plasmas except for Cu target.
These are shock waves according to steepening of
the line proﬁle in SOP(not shown). We obtained
electron density ne from interferometry and ﬂow
velocities of plasmas from Thomson scattering.
Using these parameters, ion-ion collision meanfree-paths λii of all materials are much larger
Figure 2: Experimental setup. The green line is than the width of the shock wave. Therefore,
the path of Nd:YAG laser and the blue line from these shock waves are collisionless shock waves.
target chamber center (TCC) is the path of self- Furthermore, λ of the heavier materials becomeii
emission at the wavelength of ∼ 450 nm.
longer because the calculated values of ionization
degree Z vary only within a factor of two.
ferometry with gated optical imager (GOI) (250 psgate width). We also measured one-dimensional
4 Conclusion
time evolution of the plasma by streaked interferometry with a streak camera. The self-emission Counter-streaming plasmas are produced by irrawas gated at the wave length of 450 nm using in- diating double-plane targets made of Al, C, Cu,
terference ﬁlters. We obtained two-dimensional and Pb. As a result of interaction of the plasmas,
image of self-emission with ICCD cameras (1.6 ns collisionless shock waves are generated using C,
gate width) and one-dimensional time evolution Al, and Pb. Mean-free-paths of heavier materials
with a streak camera, which is called streaked op- become longer because the ionization degrees oftical pyrometer (SOP). The plasmas were probed C, Al, Cu, and Pb are not much diﬀerent.
by Nd:YAG laser beam whose wavelength was
532 nm and duration time was 10 ∼ 14 ns. Another Nd:YAG laser beam for Thomson scattering References
was focused at the meddle of two planes. We used
triple-grating spectrometer and ICCD camera to [1] Y. Kuramitsu et al. Phys. Rev. Lett., 106, 175002(2011).
obtain spectrum of Thomson scattering.
[2] T. Morita et al. Phys. Plasmas, 17, 122702 (2010).

3Result

Two-dimensional images of self-emission for different materials are shown in Fig. 3. As shown in[3] T. Ide et al. Plasma Fusion Res., 6, 2404057 (2011).