24F06
Collisionless shock generation in an external magnetic field by using
high-power laser system
高出力レーザーを用いた磁場中における無衝突衝撃波の生成
T. Morita1 , Y. Sakawa1 , Y. Kuramitsu1 , T. Ide2 , K. Nishio3 et al.
森田太智 1 , 坂和洋一 1 , 蔵満康浩 1 , 井出尭夫 2 , 西尾健斗 3 , 桒田三沙 3 , 井手張良 3 , 坪内邦男 2 ,米田仁紀 4 , 西田明憲 2 , 並木智紀 4 , 丹治浩樹 2 , 乗松孝好 1 , 富田健太郎 5 , 中山和貴 5 ,井上和哉 5 , 内野喜一郎 5 , C. Gregory6 , 中堤基彰 6 , 中堤晴美 6 , A. Pelka6 , A. Diziere6 ,M. Koenig6 , K. Schaar7 , G. Gregory7 , S. Wang8 , D. Yuan8 , Q. Dong8 , 高部英明 1
1Institute 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
2Graduate School of Engineering, Osaka University 2-6, 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 2-6
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
4Institute for Laser Science, University of Electro-communications 1-5-1, Chofugaoka, Chofu, Tokyo 182-8585,
Japan
電気通信大学レーザー新世代研究センター 182-8585 東京都調布市調布ケ丘 1-5-15Interdisciplinary 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
6LULI, École Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau, France
7
University of Oxford, Parks Road, Oxford OX1 3PU
8Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
Collisionless shocks are produced in counter-streaming plasmas in an external magnetic ﬁeld.Theshocks are generated due to an electrostatic (ES) ﬁeld generated in counter-streaming laser-irradiatedplasmas, whose resuls have been reported previously in a series of experiments without external
magnetic ﬁeld [T. Morita et al., Phys. Plasmas, 17, 122702 (2010), Kuramitsu et al., Phys. Rev. Lett.,
106, 8 (2011)] via laser-irradiation of a double-CH-foile target. The magnetic ﬁelds are generated byputting an electro-magnet (∼10 T and β ∼ 101−4 ) near the target. The result shows no large diﬀerence
between with and without external magnetic ﬁeld in high β condition early in time (t < 25 ns).

the collisionless shock generation with an external
magnetic ﬁeld in which the plasma beta is relaThe aim of the research is to reproduce colli- tively high (β ∼ 101−4 at t < 25 ns after laser
sionless shocks as observed in supernova rem- irradiation) and is comparable to those of typicalnants (SNRs) and to ﬁnd the physics of colli- SNRs (β ∼ 103−6 ).
sionless shock formation. This also aims at thephysics of particle acceleration relating to the2 Experiment
origin of cosmic rays. We have studied collisionless shock with high-power laser-produced The experiment was performed with Gekko-XII
counter-streaming plasmas[1, 2]. These results HIPER laser system, frequency tripled Nd:Glasshave shown high Mach-number electrostatic (ES) laser (351 nm) which have the energy of ∼ 120
shock generation in high-speed counterstreaming J/beam in 500 ps with the focal spot of 300 µm
laser-produced plasmas. In the universe, usu- in diameter and the intensity of 1015 W/cm2 toally, electromagnetic shocks are observed at SNRs, produce high-velocity counter-streaming plasmas.
however, the ES shocks can be produced in a very Three laser pulses are focused on one of the inearly stage of the growth of SNRs. These experi- ner surface of a double-CH-foil target (ﬁrst-foil) asments, however, have been performed without an shown in Fig. 1 to produce high-velocity plasma
external magnetic ﬁeld. In this report, we show ﬂow. The other foil (second-foil) is irradiated by1Introduction

the radiation from the plasma generated at theﬁrst-foil, resulting in the generation of counterstreaming plasmas between two foils. The plasmas are diagnosed with a streaked-optical pyrometer (SOP) and self-emission gated-optical-imager(GOI) by observing the emission, and the shadowgraphy (SG), interferometry (IF), and the measurement of Thomson sattering (TS) using a probe
laser: frequency doubled Nd:YAG laser (527 nm)with the pulse duration of ∼20 ns and an intensiﬁed charge coupled device (ICCD) with 2 ns exposure time. An electro-magnet is placed at ∼5mm from the edge of the target to apply an external magnetic ﬁeld of ∼10 T perpendicular to thetarget normal direction.

Figures 2(a)–2(d) show the SG data taken att = 10, 15, 20, and 25 ns, respectively, with an
external magnetic ﬁeld of ∼ 10 T applied by theelectromagnet. Early in time at t = 10 ns, there
are no density jump observed by the SG, however,the clear shock image can be obtained at latertime as shown with white arrows in Figs. 2(b)–2(d). The SOP data shows the time evolution of
the plasmas as shown in Fig. 2(e). The data ofFigs. 2(b), 2(d), and 2(e) are taken in a samelaser shot. Two shocks are observed as shown withwhite arrows after t = 20 ns. In our previous result argued in Ref. [1, 2], these shocks are generated by ES potential comparing with the shock
width and formation time of them with numerical calculations[3] of particle-in-cell simulations.
More later in time (t > 25 ns), two shocks interact each other and and propagate in diﬀerent
directions (not shown in this report).
Comparing the experimental results with andwithout external magnetic ﬁeld at relatively earlyin time (t < 25 ns), there are no large diﬀerencein shock formation time and shock velocities combining the results of the GOI, IF, and SOP. Laterin time (25 < t < 60), the velocity of two shocks
Figure 1: The schematic view of the target. are diﬀerent between with and without a magnetic
HIPER laser pulses are focused on the inner sur- ﬁeld.
face of the ﬁrst foil. The magnet is placed near
the target to produce an external magnetic ﬁeld 4 Conclusion
perpendicular to the target normal direction.
We have produced ES shocks in counter-streaming
laser-produced plasmas in an external magneticﬁeld. The density jumps due to the ES shocks are3 Resultclearly observed in the SG and SOP as in Fig. 2,IF, and TS (not shown). Comparing the resultswith and without an external magnetic ﬁeld, there
are no large diﬀerence in relatively large β ∼ 101−3
at early in time (t < 25 ns).
Acknowledgments
The authors acknowledge the staﬀ at the Instituteof Laser Engineering, Osaka University. This research was supported in part by the Japan Society
for the Promotion of Science (JSPS).
References
Figure 2: The SG data taken at (a) t = 10 ns, (b)15 ns, (c) 20 ns, and (d) 25 ns, and (e) the SOP [1] T. Morita et al, Phys. Plasmas, 17, 122702 (2010).
with external magnetic ﬁeld of ∼ 10 T. The data [2] Y. Kuramitsu et al, Phys. Rev. Lett., 106, 8 (2011).
of [(a) and (c)] and [(b), (d), and (e)] are taken in [3] Tsunehiko N. Kato and Hideaki Takabe. Phys.
Plasmas, 17, 032114 (2010).
the same laser shots.