23P157-P
Study on Behaviors of Evaporated Gas in Liquid Wall Chamberof Laser Fusion Reactor II
レーザー核融合炉液体壁チェンバー内の蒸発ガスの挙動に関する研究 II
Hiroyuki Furukawa, Mitsuo Nakai1), and Takayoshi Norimatsu1)
古河裕之, 中井光男1)，乗松孝好1)
Institute for Laser Technology
2-6 Yamada-oka, Suita, Osaka 565-9871, Japan（財）レーザー技術総合研究所 〒565-0871 大阪府吹田市山田丘2-61)
Institute of Laser Engineering, Osaka University
2-6 Yamada-oka, Suita, Osaka 565-9871, 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

An integrated ablation simulation code DECORE ( DEsign COde for REactor ) has beendeveloped to analyze characteristics of plumes produced by ablation, and to clarify theability of the chamber clearance. Characteristics of a plume produced by ablation inliquid wall chamber of KOYO-fast have been analyzed. A plume produced by ablation
moves with velocities of a few km/s. Formation of clusters in a plume with hydrodynamic
motion is carried out. Diameters of clusters in a plume in liquid wall chamber ofKOYO-fast is mainly from 10 nm to 20 nm.

1. Introduction
A design of laser fusion reactor with a liquidwall, KOYO-fast, is reported in Refs. 1-3. Fig.
1 shows the simple outline of the first wall ofKOYO-fast.

Fig 2 Phenomena which occurs nearby first wall ofKOYO-fast.

Fig. 1 The simple outline of the first wall of KOYO-fast.

One of the critical issue of a laser fusion reactor
with a liquid wall is the chamber clearance. After
micro explosion with 100 MJ nuclear yield, about
10 kg of liquid metal evaporates from the surface
due to heating by  particles, ions and debris fromthe target[4]. Contribution of X-ray on the ablation isnegligible in the case of direct implosion[4]. The
evaporated plume makes, then, mist and clusters
after expansion cooling[5]. Such clusters would
attach on the injected target surface and degrade thetarget performance through RT instabilities andpreheat of the fuel. Fig 2 shows phenomena which
occurs nearby first wall of KOYO-fast.

To experimentally simulate the ablation process,laser irradiation is often used. We, however, foundthat ablation process by ions is quite different fromthat by lasers. The range of  particles in liquid Pb
is about 10 m. As the result, superficial liquid Pb
evaporates as a high density, low temperature,plasma with low ionization rate.
In this study, we have developed an integrated
ablation simulation code DECORE ( DEsign COdefor REactor ) to analyze characteristics ofplumes produced by ablation, and to clarify theability of the chamber clearance. In this integrated
simulation code, effects of condensation of a plume,the formation of clusters in the ablated plume,
phase transition from liquid to neutral gas topartially ionized plasma, absorption of energies ofcharged particles, equation of state, hydrodynamics,and radiation transport are included.

2. Results and Discussions
Fig. 3 shows number density and velocity profilesof lead at the time a plume reaches to the center ofthe chamber. As shown in Fig. 3, ablated leadmoves with velocities of roughly 40 km/s. To
estimate number density and velocity is very
important for analysis of collisions between plumes
at the center of the chamber.

1019
1018
1017
1016
1015
1014
1013
1012
1011

1.97ms
1.01ms330
Velocity

20

00.5 1

1.5 2x (m)21010Density

1100
2.5 350

1RateTime = 0.08713 ms

30

0.8
0.6Diameter

1000

6.02ms
5.03ms3.03ms10Fig. 4 shows diameters of clusters andcondensation rate at the same time in Fig. 3. The
regime x < 0.5m, clusters are created.

2041040
Time = 0.08713 ms

Fig. 3 Number density and velocity profiles of lead.

40

near by the center of the chamber, pressure isroughly 2000 Torr. Pressure near by the center are
decreasing and pressure distributes widely after
time 1.97 ms.

0.40.200.1 0.2 0.3 0.4 0.5 0.6x (m)Fig. 4 Diameters of clusters andcondensation rate
Collisions between plumes produced by ablation
at the center of the liquid wall chamber areestimated. Collisions between plumes strongly
affect a design of laser fusion reactor. Fig. 5 shows
the time development of pressure distribution. Notethat in Fig. 5, times from a collision starts aredescribed. As shown in Fig. 5, at the time = 1.97 ms,-3-2-10

12x (m)Fig. 5 The time development of pressure
distribution.

References[1] Y. Kozaki, Fusion Science and Technology 49(2006) 542-552.
[2] Y. Kozaki et.al.; J. Plasma and Fusion Research82 (2006) 817-837. (in Japanese)[3] Y. Kozaki et.al.; J. Plasma and Fusion Research83 (2007) 3-29. (in Japanese)[4] H. Furukawa, Y. Kozaki, K. Yamamoto, T.
Johzaki, and K. Mima ; Fusion Engineering andDesign73 (2005) 95-103.
[5] H. Furukawa, and T. Norimatsu, J. Plasma andFusion Research 87 (2011) 51-55. (in Japanese)3