24D17
Formation of High -R core using slow implosion method for Fast Ignition
高速点火のための低速爆縮による高密度半径積コアの形成
Hideo Nagatomo1, Atsushi Sunahara2, Tomoyuki Johzaki2, Hitoshi Sakagami3, Kunioki Mima4
長友英夫1，砂原淳2，城﨑知至2，坂上仁志3，三間圀興4
1Institute of Laser Engineering, Osaka University
2-6 Yamadaoka, Suita, Osaka 565-0871, Japan1
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2-62Institute for Laser Technology
2-6 Yamadaoka, Suita, Osaka 565-0871, Japan2(財) レーザー技術総合研究所 〒565-0871 大阪府吹田市山田丘2-6
3
Fundamental Physics Simulation Research Division, National Institute for Fusion Science322-6, Oroshi-cho, Toki, Gifu 509-5292, Japan3
核融合科学研究所基礎物理シミュレーション研究系 〒509-5292 岐阜県土岐市下石町322-6
4The Graduate School for the Creation of New Photonics Industries
1955-1 Kurematsu-cho,Nishiku,Hamamatsu,Shizuoka,431-1202, Japan4
光産業創成大学院大学 〒413-1202 静岡県浜松市西区呉松町1955-1
In the implosion phase of the Fast Ignition scheme, most critical issues are breakup of the cone tip and theformation of high R core plasma to improve its heating efficiency. Also material of the cone tip isessential for high energy electron transport. For the integrated FI experiment at ILE Osaka University,robust and reliable implosion must be redesign. In this paper, feasible target design under the constraint
condition of existing GXII and LFEX facilities is studied using two-dimensional radiation hydrodynamic
simulations, and an optimum target design based on low velocity implosion is proposed.

1. Introduction
There are some difficulties in formation of coreplasma for fast ignition scheme. Most ofimplosion design has inserted cone in shell target
to keep the heating laser pass vacuum. Therefore
the tip of the cone which is exposed in highdensity and high temperature core plasma during
the last phase of implosion should be survived
until the heating time. In FIREX-I (Fast Ignition
Realization Experiment phase I) at ILE Osaka
University, implosion design is based onconventional high density implosion experiment[1], where implosion velocity is go up to
3.0x107cm/s to obtain hot spot in the center ofcore plasma. This is not necessary condition in
fast ignition. One possibility to improve process
is the slow implosion [2] where implosion
velocity is less than 2.0x107cm/s to keep low
adiabat. In this paper a possibility of the slow
velocity implosion scheme at GXII laser in ILE isstudied
using
two-dimensionalradiationhydrodynamic simulations, and a preferable
design for FIREX-I experiment is proposed.
2. Simulations
The 2-D radiation hydrodynamic code, PINOCO[3] is used for this simulation. The laser conditions
are based on current GXII performance. The energy

and the wavelength of the direct drive laser areassumed as 3.3 kJ and 0.53 m respectively. Thetailored laser pulse is applied and its duration islimited to 4.5 ns due to the GXII limitation. In theconventional implosion, radius and thickness of thetypical shell target are 250 m and 7 mrespectively. Here, they are set to 145 m and 25
m respectively after optimization using 1-D
simulations. Robustness of the implosion isnecessary against laser non-uniformity and target
surface roughness. In this study non-uniformity oflaser irradiation are assumed as mode 6, andamplitude of 5%, which are typical numbers in
GXII facility.
Figures 1 and 2 show the temporal -R ofcompressed core plasma in cases of conventional
implosion and slow implosion respectively. The
solid lines and dashed lines indicate the implosion
with uniform laser irradiation and with non-uniform
laser irradiation respectively. In this ideal case -R
is 0.48 g/cm2 with uniform laser irradiation whereas
0.25 g/cm2 with non-uniform laser irradiation. On
the contrary, in low velocity implosion cases, they
are about 0.30 g/cm2 for both cases. In realistic
conditions, the higher mode of laser non-uniformity
and target surface roughness must be seededfurthermore and the hydrodynamic instability will
be grown exponentially. Thicker shell target of low

velocity implosion will be robust and stable against
such perturbations also.
The duration of high -R period (-R > 0.2
g/cm2) is 80 ps in conventional implosion case and
140 ps in slow implosion case respectively. This is
another advantage of low velocity implosion forfast ignition where long heating window isrequired.

It will be able to optimize using pointed cone
concept using Diamond-like-Carbon [5].
3. Conclusion
The slow implosion for fast ignition is studied
and an optimized design for FIREX-I experiment is
proposed using 2-D radiation hydrodynamicsimulations. The advantage of the scheme is not
only low adiabat implosion but also robust against
hydrodynamic instability due to the non-uniform
laser irradiation and target surface roughness. Also,
relatively longer confinement time may extend theheating window time.
Acknowledgments
These simulations were executed at Cyber Media
Center, Osaka University, and ILE OsakaUniversity. The authors would like to appreciate thetechnical staffs at CMC and ILE Osaka University.

Fig.1. Temporal averaged -R of core plasma inconventional cone-guided implosion case, withnon-uniformity laser irradiation case (dash line) anduniform irradiation case (solid line).

Fig.2. Temporal averaged -R of core plasma in slow
velocity implosion case, with non-uniform laser
irradiation case (dash line) and uniform irradiation case(solid line).

The breakup time of the tip is 4.36 ns which isslightly earlier than maximum compression time if
it is made of Au (thickness: 6 m). In this study, tipmaterial, shape, and thickness are not optimized yet.

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[3] H. Nagatomo et al., Phys. Plasmas 14 (2007)056303.
[4] D.S. Clark and M. Tabak: Nucl. Fusion 47 (2007)
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[5] A. Sunahara et al., Laser Part. Beams, to be
published.