S-2-2

Frontier of Plasma Physics Openedby Fast Ignition Fusion Research
超高強度レーザー核融合の展開するフロンティア科学
K.Mima, R.Kodama, and H. Nagatomo
三間圀興, 兒玉了祐、長友英夫
Institute of laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 Japan
大阪大学レーザーエネルギー学研究センター、〒565-0871 吹田市山田丘 2-6

Research status of ultra-intense laser plasma physics is reviewed. The related researches are on fast ignition
laser fusion with the GEKKO XII and PW lasers and the related high energy density plasma physics. Recent
new findings are generation of a very high relativistic electron current, heating of high density plasma , highenergy ion generation, and so on.
1. Introduction
Since the CPA (Chirped Pulse Amplification ) wasinvented by G. Murou etal in 1985, the short pulse
ultra-intense laser technology has developed rapidly.
The peak power of laser increased by factor 2 every year
from giga watt to Peta Watt. At present, laser peak power
reaches 1 peta watt. When such a laser beam is focused toa 10 µm x 10µm spot, the peak laser intensity is about 1021
W/ cm2 and the electron quiver energy is higher than
10MeV. This new technology open up a new laser fusion
scheme so called Fast Ignition. In the fast ignition, animploded high density core plasma with a density higher
than 1000 times solid density is instantaneously heated up
by a multi-10kJ peta watt laser. We have been studying thefast ignition scheme by the GEKKO XII and PW lasers
since 1996. In 2002, It was reported that the neutron yield
increased from 104 to 107, when a 400 J/0.6 ps PW laser
was injected into a compressed CD shell. For the progressof fast ignition research, it is necessary to understandphysics of relativistic laser plasma interactions.
Researches on relativistic laser plasma interaction are
opening a new laser fusion but also a frontier of plasma
physics such as high field science like laser particle
acceleration.
2. Ultra-intense laser plasma physics and related
computer simulations
With the simulation system, we will describe global
phenomena of the high density plasma interactions withultra intense laser and related high energy particle
generations, as shown in Fig. 1. When a peta watt laser isfocused onto a solid target, the photon pressure of theorder of 10Gb is applied to the plasma and a high density
relativistic electron beam is generated on the surface
plasma. The ultra intense relativistic electron beam (REB)
induces very strong magnetic fields through theelectro-magnetic two stream instabilities when it interacts
with dense plasmas[1]. Furthermore, the REB produces

hard X-ray, γ− ray, Mega eV electron and ion, and neutron
and meson through collisions of high energy ions andelectrons with high Z nucleus [2][3]. Those high energy
photons and particles produced by peta watt lasers areapplicable not only to fast ignition laser fusion [4][5][6],but also to nuclear science, laboratory astrophysics,
positron emission tomography (PET), heavy ion cancer
therapy, and so on [2][3]. Since the relativistic electron
generation and subsequent electromagnetic phenomena
occur in femto second time scale and sub-micron spacescale, it is extremely difficult to measure and analyze thephysical process precisely and directly by experiments.
Therefore, the data analysis assisted by various
simulations is very necessary for interpretation ofexperimental results and comprehensive understandingsof peta watt laser plasma physics. Since the high energy
particles spread over the wide area and propagate for long
distance in a long scale plasma before arriving detectors,
the large scale plasma simulations are also necessary.
The precise laser plasma interactions are simulated by amicroscopic simulation code like PIC, where the special
resolution is smaller than the dense plasma skin depth
which is less than 0.µm. If a few hundreds µm scale
plasmas are simulated by the PIC, the total number ofmesh would be 1012 which will require the memory of thecomputer greater than 100Tbits. So, the speed of thecomputer would be required faster than 100T flops. Sucha super computer does not exist yet. In order to overcome
this difficulty, we are developing a new simulation system
which consists of interconnected multi-simulation codes.
As shown in Fig.1, simulations of four codes; particle incell code, PIC-electron fluid hybrid-code, Fokker Planckcode, and hydro simulation code are coupled. The detailof the interconnection will be described in the following
report.
3. Future prospects
As the next step of the fast ignition research, we started

the FIREX (Fast Ignition Realization Experiment) project
toward demonstrating the fast ignition with a new highenergy PW laser, LFEX (Laser for Fast Ignition
Experiment) which is currently under construction. Thishigh energy peta watt laser will produce large scale andhigher energy relativistic plasmas and present newfindings in the relativistic plasma physics. In the talk, thefuture scope of the development of this research field isdiscussed.

Ultra high pressure≥10Gb

10µm
X-ray, γ ray
MeV Electron,

Peta watt laser

and Ion
NeutronMeson, Positron

Micro; PIC simulation

Tera Hz radiation

MeV electron

Fast Ignition
Laser Fusion

Energy applications

Macro ;
Hydro simulation

positron

Dense

Peta wattlaser

Fig.1

Meso-scopic ; PIC-EHydro
Hybrid, Fokker Planck code

Harmonics,
X-ray , γ ray

Medical Applications
Lab. Astro physics

High energy ion beams

Nuclear science
Unstable nuclear
generation

Physics of ultra intense laser plasma and related simulation schemesREFERENCES[1]Y. Sentoku, K.Mima, et al.: Phys. Rev. Lett., 90,1555001 (2003).
[2] V. Yu. Bychenkov, et al.: JETR Lett., 74, 586 (2001).
[3] Y.Sentoku, et al.: Appl. Phys. B ; Opt., 74, (2002) 207.
[4] R. Kodama, P. Norreys, K.Mima, et al.: Nature 412, 798(2001) .

[5] R. Kodama, et al.: Nature, 418, 933 (2002).
[6] Y. Kitagawa, et al.: Phys. Of Plasmas, 92202 (2002).