23P164-B
Optimization of Direct Drive Fuel Target in Heavy Ion Inertial Fusion
重イオンビーム慣性核融合における燃料ターゲットの最適化
Shunsuke Koseki1, Tatsuya Kurosaki1, Daisuke Barada1, Shigeo Kawata1 and A. I. Ogoyski2
古関 俊介1, 黒崎竜也1，茨田大輔1，川田重夫1，A. I. Ogoyski2
1

Utsunomiya University,7-1-2, Yohto, Utsunomiya 321-8585, Japan
宇都宮大学 〒321-8585 宇都宮市陽東7-1-2
2
Varna Technical University, Varna 9010, Bulgaria

A sufficient fusion output gain is realized in heavy ion inertial fusion by using light target materials. Fueltarget parameters are optimized to obtain the sufficient fusion energy in heavy ion inertial confinement
fusion (HIF). In this study, the target structure, the heavy ion beam (HIB) input pulse shape and the HIB
input pulse energy are optimized. We performed two-dimensional fluid implosion simulations to obtain ahigh pellet gain. The optimized target shows a gain 223. The input Pb beam energy is 1.8MJ.

2. Optimization of target structure and HIB
pulse shape
Figure 1 (a) shows the fuel target in our previouswork [7-10]. This target consists of Pb and Al as atamper and a HIB-energy absorber, respectively[7-10]. Figure 1 (b) shows a lightened fuel target.
This target consists of Al and C as a tamper and aHIB-energy absorber, respectively [11]. Figure 1 (c)shows the input pulse which we used for each target.
We call the low pulse power in the input pulse afoot pulse and the high pulse power in the input
pulse a main pulse. The input Pb beam energy is
4MJ. When the fuel target in our previous work isused, we obtain a gain 52.6. A high gain can beachieved by the light-material of tamper (Al) andHIB-energy absorber (C). By the light-material
target, we obtained a gain 61.9.
The foot pulse duration is designed so that the main
shock by the main pulse overlaps at the inner edgeof the DT liquid fuel with the first weak shock tominimize the DT fuel preheating. Therefore, weperform a parameter study for the foot pulse
duration for Fig. 1 (b). When the foot pulse durationis changed from 16ns to 22ns, the irradiation for themain pulse starts after 2ns of the foot pulse end.
The HIB input energy is fixed to 2MJ, and the main
pulse duration is changed to keep the HIB totalenergy. The maximum gain is at 19ns for the footpulse duration (see Fig. 2).
(a)

(b)

4.00mm

4.00mmAlPb
3.971mm3.971mm
Al
2.69g/cm3
3.503mm
CAl Foam
0.00269g/cm3
2.903mm
3.471mm
Al
2.69g/cm3DT
2.830mmDT
0.19g/cm3
3.363mm Void
2.690mm
Void
11.3g/cm3

2.69g/cm3
2.26g/cm3
0.19g/cm3(c)Beam Power [TW]1. Introduction
Research issues in heavy ion beam (HIB) inertial
confinement fusion (ICF) include beam bunching,
HIB transport in a reactor, non-uniformity of beamirradiation, implosion uniformity, implosion
efficiency, energy gain and so on. In fuel target
implosion, ICF has two ways of implosion schemes,that is, indirect-driven scheme and direct-driven
implosion scheme [1-6].
In this paper, we focus on a direct-drive scheme,
and we present an improvement of the pellet gainby the optimization of the target structure and theHIB input pulse shape. As a result, we obtained apellet gain 223 by optimizing the target structure,
the HIB input pulse shape and the HIB input pulse
energy.

Time [ns]Fig.1. Target structures (a) consists of Pb and Al as atamper and a HIB-energy absorber, respectively, and (b)consists of Al and C as a tamper and a HIB-energy
absorber, respectively. (c) HIB pulse shape used for eachtarget.

Fig. 2. The pellet gain versus
the foot pulse duration.

The energy-absorber thickness is decided bychanging the inner radius of energy absorber layer.
We change the C thickness from 400µm to 700µmand set the optimal foot pulse duration in the pulse
shape for each thickness of energy absorber (C).
When the C thickness is thin, the interception of theheat that enter the DT fuel layer becomes difficult.
However, when the C thickness is thick, the pellet
gain becomes lower. When the thickness of energy
absorber is 500µm, we obtain the gain of 137 (seeFig. 3).

3. Conclusions
In this paper, we discussed the improvement of
the pellet gain by the light-material target structure,
the optimizations of the HIB input pulse shape andthe HIB input pulse energy. The optimized target
structure consists of the Al thickness 30µm and theC thickness 500µm as a tamper and a HIB-energy
absorber, respectively. We obtain the higher gain inthis study, compared with that for theheavy-material target (see Fig.1 (a) ). In the near
future, a robustness of the target implosion against
the implosion nonuniformity should be studied.
Acknowledgment

Fig. 3. The pellet gain
versus the thickness ofenergy absorber (C).

We change the main pulse power from 186TW
to 436TW for Fig. 1 (b). When the main pulsepower is high, the pre-heat on the DT fuel layer
becomes large. When the main pulse power is weak,
implosion velocity in the DT fuel layer do not
become a sufficient speed. When the main pulse
power is 336TW, we obtain the maximum gain inthis case (see Fig. 4).

Fig. 4. The pellet gain
versus the main pulse
power.

We change the HIB input energy from 1.4MJ to
2.0MJ for Fig. 1 (b). When the HIB input energy
become large, the pre-heat in the DT fuel layer
becomes significant. When the HIB input energy issmall, the efficient implosion is not possible,because the implosion velocity in the DT fuel layer
does not become a sufficient speed. When the HIB
input energy is 1.8MJ, we obtain the gain of 223(see Fig. 5).

Fig. 5. The pellet gain
versus the input energy.

This work was partly supported by the JSPS
(Japan Society for the Promotion of Science) andMEXT (Ministry of Education, Culture, Sports,Science and Technology) and CORE (Center for
Optical Research and Education, Utsunomiya Univ. ,Japan). We would also like to present our thanks tocolleagues in the Japan and US HIF VNL researchgroups for their fruitful discussions on this subject.
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