SII-2
高出力レーザーによる飛翔体の加速と惑星科学への応用
Flyer Acceleration by High-Power Laser and Applications to Planetary Science
門野敏彦1，境家達弘2，重森啓介3，弘中陽一郎3，他
T. Kadono1, T. Sakaiya2, K. Shigemori3, Y. Hironaka3, et al.
1

産業医科大学，2大阪大学大学院理学研究科,
3
大阪大学レーザーエネルギー学研究センター
1
Univerisity of Occupational and Environmental Health, 2Faculty of Science, Osaka University,
3
Institute of Laser Engineering, Osaka University
Introduction

Experiment
Our acceleration method is as follows. High-power laser,
GEKKO XII at Institute of Laser Engineering of Osaka
University (ILE), irradiates spherical or sheet flyers. The
surface of the flyers vaporizes and becomes
high-temperature and pressure plasmas. The expansionof the plasma causes the acceleration of the flyers. We
have carried out the experiments with various flyer
shapes, sizes, and materials [1-4]．
The velocity of the flyers was measured using a streak
camera [1-2]. Simultaneously, using a framing camera,
we took the images of the flyers and confirmed the shapeof the flyers during the acceleration [3-4]．
Using this acceleration method, impact experimentswith rocks were conducted. As measurement methods,VISAR, a streaked optical spectrometer, X-ray pin-holecameras, and a quadrupole mass spectrometer, were used.
Also, we recovered the targets after the laser shots, andanalyzed craters, fragments, and the inside of the craters
in detail.

ResultWe have succeeded to accelerate aluminum (Al), glass,gold (Au), and diamond spherical projectiles, andtantalum (Ta) sheet flyers. In Fig. 1, we show all results

100Flyer velocity [km/s]

Hypervelocity impacts of meteorites at velocities
exceeding 10 km/s occurred on the surfaces ofproto-planets. Such impacts would cause a large amountof silicate vapor, which should play very important rolesin the origin and evolution of atmosphere, ocean, and life.
To quantitatively investigate such impact phenomena inlaboratories, flyers larger than sub-mm in size arenecessary for present measurement and analysis systems.
However, it has been difficult for previous acceleration
facilities to accelerate flyers with such sizes to velocities
higher than 10 km/s. Recently, we have developed a new
acceleration method of spherical and sheet flyers with asize of sub-mm and succeeded to accelerate these flyers
to velocities exceeding 10 km/s. Here, we show the flyer
velocities obtained by this method and introduce someplanetary applications now proceeding.

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102E/m [J/kg]
pFigure 1. Flyer velocity as a function of laser energy over flyer
mass. Close and open symbols denote spherical projectiles andTa sheet flyers, respectively. The transfer efficiency from laser
energy to kinetic one in the case of sheet flyers is higher (~0.1-1 %) than that of spheres (~ 0.1-0.01 %).

of the acceleration experiments [1-4]. The vertical axis is
the flyer velocity V [km/s] and the horizontal axis is
2E/mp [J/kg] in log-log form, where E and mp are thelaser energy and flyer mass, respectively. If the ratio oflaser energy to flyer kinetic one is constant, the velocity
should increase linearly with a slope of 1/2 in this plot.
We show three lines with a constant transfer efficiencyof 1 %, 0.1 %, and 0.01 %. The experimental resultsindicate that, though there are some scatter, the slope isroughly 1/2, and that the efficiency is ~0.1-0.01 % for
the spherical projectiles and ~1-0.1 % for the sheet flyers.
Also, Al projectiles are more efficiently accelerated than
the glass ones, and the efficiency of the Au ones is lessthan 0.01 %.

REFERENCES

Application
Using this acceleration method, various impact
experiments are proceeding as follows.
（１） Equation of state of minerals at high pressuresand thermo-dynamic states of vapor caused byimpacts [5-7] (Collaboration with University ofTokyo (UT), Institute of Space andAstronautical Science (ISAS), Planetary
Exploration Center, Chiba Institute ofTechnology (PERC), and ILE)
We obtain the Hugoniot equation of state of Forsteriteand Diopside at a few hundreds GPa by measuring shock
velocity and/or particle velocity using VISAR. Also, weinvestigate the thermodynamic states of vapor, released
from the high-pressure states, using time-resolved
spectrometers.
（２） The composition of impact generated vapor andits implication to the K/Pg mass extinction
event [8] (Collaboration with PERC, UT, andILE)
It is known that the impact would play important roles in
the K/Pg mass extinction, but the mechanism has notbeen clear. We carry out the impact experiments withanhydrate and investigate the composition of generated
vapor (SO2 and SO3). The result reveals the mechanismof the extinction.
（３） Crater size and scaling law (Collaboration with
Kobe University (KU) and ILE)
Crater size, the most basic physical quantity impact
cratering, is investigated. We verify and improve theaccuracy of the scaling laws previously established on
the basis of the data below 10 km/s.
（４） Size distribution of fragments [9] (Collaborationwith KU and ILE)
The sizes of recovered fragments ejected from craters aremeasured. Comparing the results with the previous dataobtained below 10 km/s, smaller fragments are relatively
dominant.
（５） Shock attenuation and recovery of shockedmaterials (Collaboration with Osaka University(OU) and ILE)
The free surface velocity of rear surface of thin rocksamples is measured by VISAR and the shock pressure isestimated. Varying sample thickness, the pressure
attenuation rates are evaluated. Also, from the analysesof recovered shocked samples, the morphology change
as a function of the distance is investigated. The colorand crack distributions indicate the pressure decreases
with the distance.
（６） Organic materials in impacts (Collaborationwith OU and ILE)
The impact experiments with meteorites are carried out
and the composition of generated vapor and recoveredmaterials in condensed phases is investigated.

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