Laser Fusion Research with GEKKO XIIand PW Laser System at Osaka

Yasukazu IzawaInstitute of Laser Engineering, Osaka University

20th IAEA Fusion Energy ConferenceNovember 1 - 6, 2004Vilamoura, Portugal

Co-authorsILE OSAKA

K. Mima, H. Azechi, S. Fujioka, H. Fujita, Y. Fujimoto, T. Jitsuno, T.Jozaki, Y. Kitagawa, R. Kodama, K. Kondo, N. Miyanaga, K. Nagai, H. Nagatomo, M. Nakai, K. Nishihara, H. Nishimura, T. Norimatsu, H. Shiraga, K.Shigemori, A. Sunahara, K. A. Tanaka, K. Tsubakimoto (Institute of Laser Engineering, Osaka University)

Y. Nakao (Kyushu University)

H. Sakagami (University of Hyogo Prefecture)

P. A. Norreys (Rutherford Appleton Laboratory)

R. Stephens (General Atomics)

D. Meyerhofer (LLE, Univ. of Rochester)

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Outline

1) Fast ignition experiment by cone-shell target

2) FIREX project and a new heating laser 10kJ, PW LFEX

3) Toward FIREX�code development�basic experiments on hot electron transport �suppression of Rayleigh-Taylor instability

4) Summary

1

10

100

10Lase Energy�iMJ�j

0.1 1

US-NIF

KOYO (Osaka design)

Fusi

on G

ain

Central Ignition

�ŸFast ignition: Processes for compression and ignition are separated.

Central ignition

Fast ignition

Laser irradiation Compression Ignition Burn

PW laser

Fast heating of compressed fuel to create a hot spot at its edge

Fast Ignition

Required gain for reactor

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Fast ignition concept is attractive, because a high gain is expected by small size laser

In fast ignition, a highly intense laser is injected into a compressed fuel.

ILE OSAKACritical issues in fast ignition: Efficient heating of the core plasmas overcoming the nonlinear interactions with the long scale plasmasurrounding the core.

Fast ignition requires to deliver ultra-intense heating pulse close to the core.

A hollow cone prevents the heating pulse from nonlinear interactions as well as energy loss in long scale length plasmas. The heating pulse can be injected to the position very near to the compressed core.

Cone

Laser

Corona plasma

Compressed core

Laser

Hot electron

Hot electron generation

�Hole boring and heating by separate laser pulsesK. Fujita et al., SPIE 4424, 37 (2001)

�Hole boring and heating by one laser pulseY. Kitagawa et al., submitted to PRL (2004)

�Cone-guiding: cone-shell targetR. Kodama et al., Nature 412, 7989 (2001),R. Kodama et al., ibid. 418, 933 (2002)

Is the high density compression possible by non-symmetry cone-shell target?

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High density compression was realized with the cone-shell target.

The compressed density obtained with the cone-shell target could be consistent with the scaling of the 1000 times compression with spherical shell targets.

GEKKO XII9 beams

for implosion

Compressed coreAu cone

Initial shell

Cone-shell target (CD plastic shell)

X-ray image of compressed core

R. Kodama et al, Nature 412, 798 (2001)

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Neu

tron

Yie

ld

Heating Laser Power (PW)

15%

Heating efficiency: 30%

108

106

1040.1 1

Ignition equivalent laser intensity

Cone shell target

PW laser 1.053µm

GEKKO XII 9 beams 0.53µm 1.2 kJ / 1ns

Au coneplastic shell

Fast ignition experiments by the PW laser demonstratedthe heating efficiency of 20%.

Enforced heating was realized at a heating power equivalent to the ignition condition.

2.25 2.35 2.45 2.55 2.65

Neu

tron

Sig

nal (

a.u.

)

Energy [MeV]

0

1.0

0.5

b

FWHM: 90±5keV keVResolution:50 keV

0.86 ±0.1 keV

500J500fs

Neutron time-of-flight

(CD shell)

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Enhancement of neutron yield indicates that the fast heating is possible during the stagnation.

Heating was realized in the time duration of less than 100ps at near the maximum compression.

500µm

0

100

200

-200 -100 0 100 200

Enha

ncem

ent o

f Ny

(a.u

.)

Av.

Den

sity

(g/c

c)

Injection Timing (ps)

0

10

5

a

Time

ILE OSAKA

FIREX : Fast Ignition Realization Experiment

1995 - 1999�GEKKO MII CPA (25J, 0.4ps, 60TW)�PWM laser (70J, 0.7ps, 100TW)

Elementary physics related to fast ignitor (laser hole boring, super-penetration, MeV electrons, Self-guiding, Cone-guiding)

1999 - 2002�PW laser (700J, 0.7ps, 1PW) + GEKKO XII

Heating of imploded plasma up to 1keV by cone-guiding

2003 - 2008 : FIREX-I (Phase 1)�New heating laser (10kJ, 10ps, 1PW) + GEKKO XII

Heating of cryogenic target to 5 ~ 10keV

2009 - 2014 : FIREX-II (Phase 2)�New compression laser (50kJ, 350nm) + Heating laser (50kJ, 10ps)

Ignition and burn, gain ~ 10

�@

�@

Existing GEKKO-XII

Laser bay

Gear room

Pre amp.

Main amp.

CompressorFocusing system

FIREX-I: Achievement of ignition temperature

Program of Fast Ignition Realization Experiment FIREX Phase I: FIREX-I Heating to Ignition temperature Phase II: FIREX-II Demo of ignition&burn

Target room I

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LFEX (10kJ, 1PW) for FIREX-I is under construction.

Output energy 12kJ/4beams (chirped pulse)10kJ/4beams (compressed)

Wavelength 1063nmPulse shape 10-20ps (FWHM)

Rise time 1-2psFocusability 20µm in diameter (50% efficiency)Prepulse < 10-8

10kJ PW laser

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2.5 kJ /1-10 ps

3.2 kJ / 2 ns

Front end(existing)

OPCPA

Booster amplifier CompressorRod amplifier

Focusing optics

Rod amplifier

Timing adjuster

Fast phase adjuster Adaptive mirror

(in beam phase correction)

Adaptive mirror(beam-to-beam phase locking)

Basic configuration of 10 kJ, PW laser�4 pass booster amplifier with angular multiplexing�adaptive optics for precise phase control�arrayed dielectric grating in large scale�4 beam combining to a single focal spot

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Spatial filter

Amplifier head

End mirror

Fore focal plane

Back focal plane1st pass

2nd pass

Input

Deformable mirror

Pick-up mirror

2-mrad angular multiplexing

(0.5-mrad longitudinal multiplexing)

3 kJ/2.3 ns∆λ = 3 nm

2x2x8 disk amplifiersBeam size: 40 x 40 cm in each beam

Beam transferin each four pass amplifier

Beam path of 4-pass amplifier by angular-longitudinal multiplexing

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GEKKO XII

10kJ, PW laser LFEX

OS 75S

OS 125S

DA 400S

SF 400S

DFM 125

DFM 75RA 50

Main amplifier chain for LFEX

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∆y∆z

x

y

zθzθy

θx

1st grating

2nd grating

Ti: sapphire CPA beam

Monolithic grating

200 fs

2nd order auto correlation trace

Far-field pattern

Arrayed grating

200 fs

optimized

Test of arrayed grating started.

(Arrayed)

Preliminary experiment

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Roof mirror

Off-axis parabola mirror

GEKKO XII target chamber

Beam monitor

F/~4.5

Beam combining/focusing geometry depends on the possible performance of a large-aperture parabola mirror.

80% 60%

20 µm

d = -160 µm -110 µm -55 µm 0 µm

Single-beam phase aberration λ/5 Beam-to-beam phase jump λ/5

Layout of beam combining / focusing optics

�Phase control less than λ/5 is required for high focusability.

Collective PIC code

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FI3 (Fast Ignition Integrated Interconnecting) Code was newly developed. ( IF/P7-29)

• The cone-guided implosion dynamics is calculated by PINOCO. and the mass density, temperatures, and other profiles calculated by PINOCO are exported to both collective PIC and RFP-hydro code for their initial and boundary conditions.

•The relativistic laser plasma interaction inside the cone target is simulated by collective PIC code FISCOF1, which exports the time-dependent energy distribution of fast electron to REP-hydro code.

• The fast electrons calculated by the FISCOF1 are exported to the RFP-hydro code. Therefore, the core heating process is simulated using both physical profiles of imploded core plasma and fast electron as the boundary conditions.

•Those numerical codes are executed on the different computers via DCCP, TCP/IP network communication tools.

The first numerical fast ignition simulation was performed to demonstrate the FI3 and to investigate the GXII experiment.

Radiation-hydro. Code (PINOCO)

(cone-shell implosion)

Collective PIC codeFISCOF1

(laser plasma interaction)

Relativistic Fokker-Planck-hydro code

(hot electron transport)

Data flow in FI3 system. (Black arrows are already executable data flows, and gray arrows are next plan to be considered.)

Code development

H. Nagatomo et al., IAEA-CN-94/IF/P7-29

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In the spherical implosion, the shell target reach the maximum compression at 2.285ns. In non-spherical implosion case, the shell continued to be compressed since a hot spot is not formed and an average ρR reached a higher value (0.15 g/cm2).

mass density

Time dependence of angular average ρR in gold cone-guided implosion (GXII scale CH target).

electron temperature

Imploded core plasma ρR is higher for cone target than for spherical target in PINOCO-2D simulations.

H. Nagatomo et al., IAEA-CN-94/IF/P7-29

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Compressed-core profile by PINOCO Implosion simulation of a cone-shell target

(2D ALE code “PINOCO” by Nagatomo)

RFP-Hydro simulationsREB was injected at inner surface of a gold cone.

H. Nagatomo et al., IAEA-CN-94/IF/P7-29

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CH shell:1000 µmφ25 µmt, D2 0, 5 atm

Laser:35 beams15 kJ/1 ns SQ(8x1015W/cm2 )

70deg Au cone

10 ps X-ray frame Image (MIXS)

Plasma streams out of hot spot.

Hot spot appears to flow out toward the cone tip.

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0 2 4 6 8 100.01

0.1

1

10

100f (

E) [a

.u.]

100nc 2nc

Energy [MeV]

Fast electron energy distribution at a top of cone.This result is used for Fokke- Planck simulation

H. Nagatomo et al., IAEA-CN-94/IF/P7-29

ILE OSAKA

IL,max = 1x1020 [W/cm2]

0 1000 2000 3000 4000 50001025

1026

1027

1028

Cor

e he

atin

g ra

te [W

/cm

3 ]

Time [fs]

ner = 2nc ner = 100nc

Core Heating Rate

0 1000 2000 3000 4000 50000.30

0.35

0.40

0.45

0.50

0.55

Cor

e Te

mpe

ratu

re [k

eV]

Time [fs]

<Te> <Ti>

ner = 2nc

ner = 100nc

Core Temperature

n = 100nc n = 2nc

Resultant core temp., <Ti> 0.43keV 0.50keV

Coupling efficiency in the case of n = 2ncfrom fast electrons to core is 25%, and from laser to core is 5.4%.

Integrated simulation results oncore heating rate and temperature

Y. Nakao et al., IAEA-CN-94/IF/1-5

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Heated blackbody emission was observed by HISAC.

Laser focused at 1019 W/cm 2

Plane target (Al)

Rear of the target is heated up by hot electrons.Black body emission was observed with time and spatial resolution.

Number of filaments decreases with increase of laser intensity and also with decrease of target thickness.

Hot electron generation and transport

HISAC: Framing camera with ∆t = 30 psec and ∆x = 30 micron.

K. A. Tanaka et al., IAEA-CN-94/IF/1-4RaY. Tohyama, R. Kodama et al., submitted to PRL (2004)

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Number of filament decreases quickly with increasing laser intensity.

Number of filament and peak brightness in rear emission were measured by 200 µm Altarget changing the laser power up to near PW. The filament could merge due to magnetic field generated by inhomogeneous conductivity,which depends on the temperature and/or heating power.

Hot electrons can be transported not breaking into filaments at the laser power of ~PW and be maintained in a flux to heat the core.

K. A. Tanaka et al., IAEA-CN-94/IF/1-4Ra

Rayleigh-Taylor Instability

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γ = kg1 + kL

− βk Ý m ρa

k: wavenumber of perturbation g: gravity L: density scale length

β was estimated by measuring all parameters.

RT growth rate by Takabe formulam: mass ablation rate ρa: mass density β: numerical coefficient

10 100

2

1

0

Wavelength (µm)

Gro

wth

rate

(1/n

s)

�@�¡�@�@�@expÕt�@�@�@�@�@β = 1.7�@�@�@�@�@

β = 5

0 10 100

3

2

1

0

Gro

wth

rate

(1/n

s)

�¡ �Ÿ�@ expÕt�@�@�@�@β = 1.7�@�@�@�@β = 6

0

0.53 µm laser 0.35 µm laser

Wavelength (µm)

exp’tβ = 1.7β = 6

exp’tβ = 1.7β = 5

β = 1.7 for shorter wavelength of perturbation.β ~ 5 for longer wavelength.

→ H. Azechi et al., IAEA-CN-94/IF/1-1Ra

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Two suppression schemes for RT growth were proposed.

3

4

5

6789

10

Gro

wth

Fac

tor

1. 61. 20. 8Ti me ( ns)

: Single-color (λ= 1/3 µm) irradiation: Two-colors (λ= 1/3 and 1/2 µm) irradiation

Rayleigh-Taylor Rayleigh-Taylor growth rate is reduced bygrowth rate is reduced by two-color laser irradiation. two-color laser irradiation.

Reduction of Rayleigh-Taylor Instability Growth with Multi-Color Laser Irradiation

Streaked image

1 ns 100 µm

one-color

Two-color (1/3+1/2-µm )

0.8 1.2 1.6 Time (ns)

25

20

15

10

5

0

Gro

wth

fact

or

2.52.01.51.00.50.0Time (ns)

CH

CHBr

→ H. Azechi et al., IAEA-CN-94/IF/1-1Ra

�Double ablation by high-Z doping: ablations by electron and radiationincrease of ablation velocity

�Two-color irradiation: enhancement of nonlocal heat transport of electron increase of density scale length

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Summary

1�Enforced heating of imploded plasmas has been demonstrated by using cone-shell targets.

2�We have started the FIREX project towards ignition and burn of laser fusion.

�FI3 (Fast Ignition Integrated Interconnecting) code was developed for target design.

�Cone-target implosion and hot electron transport have been studiedby the experiment and simulation.

�New stabilization schemes for R-T instability were proposed andsignificant suppression of instability were demonstrated.

� A new heating laser LFEX,10kJ/10ps PW laser,is under construction. Technical issues should be solved such as segmented grating andphase coupling.

�Foam cryogenic cone-shell target is under development.

3�FIREX-I experiment will start before 2007. Gain of up to 0.1 will beexpected at FIREX-I.

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Laser fusion research is progressing towardignition and burn.

Ion temperature�iK�j

‰Á”M‚Ì�uŠÔ

�@

Nova

1022

1021

1020

1019

1018

106 107 108 109(

FIREX-I

FIREX-II

NIFGEKKO XII High densitycompression '88-89

GEKKO XII LHART '85-86

GEKKO IV '80-81

GEKKO MII '80

Fast ignition '02

Ignition

Fusi

on p

aram

eter

�is

ec/c

m3

�j

High gain

10 100 10000.1

1

10

100

Total Driver Energy [kJ]

ρ = 300 g/ cc and α = 2

FIREX-II

Experimental reactor LFER

Solid wall reactor

FIREX-Iρ = 300 g/cc, α = 2

Liquid wall reactor

Targ

et g

ain

IREB (1020W/cm2) FIREX-II 1.4 IFER 1.4 Solid 2.6 Liquid 2.6

Reactor technology: see Y. Kozaki et al., IAEA-CN-94/IF/P7-5