Inertial Confinement Fusion and Related TechnologyTatsuhiko Yamanaka
Institute of Laser Engineering, Osaka University
2-6 Yamada-oka, Suita, Osaka, 565, Japanand -1.5 pm respectively. Figure 2 shows the progress andprospect oflaser fusion u.

Abstract
Present status with future prospects and related
technologies of the inertial confinement fusion aredescribed. The required temperature and density of plasma
have been achieved independently using 10 kJ laser
system. 100 kJ laser with the wavelength of 350 nm could
demonstrate the break even condition of fusion.

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Etoae _AMor- 80<II·o 4Introduction
If we want to achieve the enough fusion gain by
imploding a DT solid fuel pellet with several MJ energy
driver or laser, a 10 3 times liquid DT density plasma withaverage temperature of less than keV is required. Where
the laser efficiency of 10 % and the coupling efficiency fromlaser to fusion plasma of 10 % are assumed. The reason
why we need such a high density, low temperature plasma
is that the required laser energy to produce a plasma withthe fixed gain is proportional to inverse square of theplasma density and to plasma temperature 0 . The plasma
with temperature of less than 5 ke V never ignites even if
the density is high enough. For ignition of fusion we haveto produce plasma with high temperature core at the centerof the fusion plasma, a particles from which heat thesurrounding cold main fuel.
From the above arguments the following issues arecoming out. 1) How much fraction of laser energy isabsorbed at the surface of the fuel pellet? 2) How
percentage of absorbed laser energy is transfered to thefusion plasma produced by the implosion process? 3) Is it
possible to produce the high temperature enough for fusion
reaction? 4) Is it possible to create 10 3 liquid DT density
plasma with low temperature preventing thehydrodynamic instability in the compression phase. Thoseare the first step of ICF and can be studied using a 10 kJclass laser system.
The second phase is the demonstration of ignition
plasma where the fuel is heated up to higher temperatureby the a particles of DT reaction. For this we have toproduce the plasma with pRof0.3 g/cm 2 and temperature of
5 ke V, where the pRof 0.3 g/cm 2 is the range of a particle.
The required energy for this experiments is estimated to be
100 kJ at the wavelength of 350 nm. Final issue in plasma
physics is the demonstration of high fusion gain plasmausing a mega joule laser or other energy drivers such as
light ion beam (LIB) and heavy ion beam (HIB). Forcommercial reactor development we have to develop
efficient, repetitive energy driver.
Here we describe the present status and some future
prospects of ICF and the spin-off as the relatedtechnologies.

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Ablated Mass I Initial MassFig. 1 The experimental hydrodynamic efficiency ,llh iscompared with the rocket model as a function ofablated mass/initial mass.

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Present status and future prospects

6The laser wavelength scaling on absorption coefficientof plasma was completely studied and showed that the laser
energ~ is absorbed more than 90% at laser intensity of 10 14W/cm for wavelength of 530 and 350 nm which are thehigher harmonics of 1 Jlm glass laser 2 '. 6% ofhydrodynamic efficiency was demonstrated by Gekko XII
experiments, which is the energy transfer coefficient fromabsorbed laser energy at pellet surface to energy of thecompressed fusion plasma as shown in Figure 1 3 '.
Temperature of 10 keV and 10 13 DT neutron yield whichcorrespond to the fusion output energy of 11500 of used laser
energy were achieved using the 10 kJ, 530 nm laser 4 '. In
the experiments glass microballoons filled with DT gas
were used. The diameter and wall thickness were -1mm

REDLaser Energy (KJ)

Fig. 2 Progress and prospect of laser driven fusion. The
solid circles are from experiments with Gekko lasers
and Nova laser, while the open circles are from thepresent simulation. This figure suggests thepossibility of breakeven experiment by 100 kJ classblue laser system.

-1-The high density compression have been recently
demonstrated using a CDT(Si) shell target with diameter of
0.5 mm at ILE Osaka as shown in Figure 3. The density
was determined from the measured areal mass density pRand mass of fusion plasma, where p and Rare the density
and radius of plasma. The pR was measured by siliconactivation method. In which the Si tracers are activated to28 Al by the 14 MeV DT neutrons. The amount of activated
Si is proportional to DT neutron yield and pR. The mass ofcompressed fusion plasma was determined by measuring
the ablated mass. The obtained density is over 600 times ofsolid density which corresponds to 4 times higher density of
the center of the sun. Figure 4 shows the achieved plasma
region by Gekko XII in the usual m-T diagram.
From these experimental results and the theoreticalresearch with aid of computer simulation we have been
confident that 100 kJ blue laser(,\= 530 nm) could achieve
the ignition or breakeven condition. The design andrequired technologies to fabricate 100 kJ laser arecompleted already.
As for the mega joule energy driver US people are doing
R & D research, and the construction will start from 1991
FY. For reactor driver a semiconductor laser pumped solidstate laser is studying which could work with the efficiency
of more than 10% and high repetition rate of about 10 Hz.
KrF laser, free electron laser, LIB and HIB are stillcandidate for the reactor driver.

Density(g I em 3) r-0:=:--7-0-:0-!-l-n-l<j>-,-:N-:o-r_m_a-:1-:L-a-s-er-:B:-e-a_m_ _ _ _,8700!-lm<j>, Random Phased Beam

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ICF related technologies
Inertial confinement fusion (ICF) using a high power
pulsed laser could open the new technological fields usefulfor scientific research and industrial applications as well as
the release of new energy. The laser produced midium
atomic number plasmas have been used successfully for xray laser midium. The super dense plasmas produced byimplosion have provided the interior of stars on the earth.
This could be useful to understand the physics in the stars.
High power laser could realize a new particle accelerator.
Plasma wave excited by the beat wave of high power laser
is one method. Another is the use of free electron laser(FEL) for the acceleration field. Of course FEL is acandidate of fusion energy driver. A peta-watt femtosecond laser which could achieve the power density over the1020 W/cm2 at the focal point might open the new methods
in the nuclear physics research. Femto-second lasers of
10 17 w/cm 2 have already opened the new area in the atomicand molecular physics. The technologies developed
relating to the fusion lasers have been contributed to theindustrial technologies. In the contray the accelerator
technology could contribute the heavy ion beam fusion
driver which is the alternative oflaser.

Shell Thickness (~Jm)
Fig. 3 Achieved density vs pellet shell thickness. CDT(Si)plastic shell targets are used.
Laser: Gekko XII 530 nm, 9 kJ, in rectangular pulse.
Random Phased Beam: special distribtution of laser
intensity on pellet is improved using R.P.P.
Normal Laser Beam: not improved.

1-D simulation(50kJ);:;E10150'0Q).!!!-...
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References.,

1014~1) T. Yamanaka; Energy and Resources 10, No2 (1989) pp58-64inJapanese.
2) For example, The Rev. Laser Engi. 14, No12 (1986).
3) S. Nakai et al.; 12th Int. Conf. Plasma Phys Conti. N ucl.
Fusion Research, B-I-1, (Oct. 1988) Nice Franceand S. Nakai et al.; "Laser Interaction with Matter"
ed. G. Velarde et al., p.90 (1989) World Scientific.
4) C. Yamanaka, et al.; Nucl. Fusion 27, (1987) 19.

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110100ion temperature Ti (ke V)
Fig. 4 Achieved Plasma region in m- T diagram usingGekko XII laser at ILE Osaka.

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