Review of Fast Ignition

HEDLP Workshop Washington

Michael H. KeyLawrence Livermore National Laboratory

August 25 to 27, 2008

Work performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under

Contract No. W-7405-ENG-48.

UCRL-PRES-

K. Akli2, F. Beg5, R. Betti6, D. S. Clark1, S. N. Chen5, R.R. Freeman2,3

S Hansen1,S.P. Hatchett1, D. Hey2, J.A. King2, A. J. Kemp1, B.F. Lasinski1 B.Langdon1,T. Ma5, A.J. MacKinnon1, D. Meyerhofer10, P.K. Patel1, J. Pasley5 R.B. Stephens4, C. Stoeckl6, M. Foord1, M. Tabak1, W. Theobald6, M. Storm6

R.P.J. Town1, S.C. Wilks1, L. VanWoerkom3, M.S. Wei5, R. Weber3, B. Zhang2

1Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

2Department of Applied Sciences, University of California Davis, CA 95616, USA

3Ohio State University, Columbus Ohio, 43210 USA

4General Atomics, San Diego, CA, 92186, USA

5 University of California, San Diego, San Diego, CA, 92186, USA

6Laboratory of Laser Energetics, University of Rochester, NY, USA

Special thanks for advice and information :

Mike Dunne, Wolfgang Theobald, Javier Honrubia, Hiroshi Azechi,

Riccardo Betti

Acknowledgements

Outline

•Concept of FI •Ignition requirements and gain

•Cone coupled electron FI

•Channel electron FI

•Proton and mid Z ion ignition

•Major integrated experiments

•Summary

Fast Ignition is ICF with separate compression and ignition drivers

10 kJ, 10 ps

Hole boring Ignition

1 MeV electrons heat DT fuel to10 keV 300 g/cc

Fast ignition

Light pressure bores hole in coronal plasma

• Laser hole boring and heating by laser generated electrons was the first FI concept

• 1MeV electron range matched to ignition hot spot

• Absorption of intense laser light produces forward directed electrons

• e-beam temperature = ponderomotive potential

100 kJ, 20 ps Hole boring

for laser to penetrate close to dense fuel

Pre-compressed fuel 300 gcm-3

M Tabak, S Wilks et al. Phys. Plasmas1,1626, (1994)

Las

er

2D simulations ofignition and burnby 15kJ, 2MeV,20µm, 15ps e-beam

0 0.5 1 1.5 2 2.5

50

100

150

200Maximum FI gain at 300g/cc

100kJ PW

200kJ PW

Several modeling studies have confirmed that FI offers high gain at low driver energy

e.g. R. Betti, A.A. Solodov, J.A. Delettrez, C. Zhou, Phys. Plasmas 13, 100703 (2006)

Driver Energy (MJ)

Ga

in

>100x gain with 500kJ driver is attractive for IFE

Laser

Au cone

The cone coupled FI concept provides a clear path for the laser with the electron source close to the ignition spot

100m

<R>DT=2.2 g cm-2

Radiation - hydro simulations are well developed for ICF and allow hydro--design optimization for FI

S Hatchett et al. - 30th Anom. Abs. Conf. Maryland, May 2000

15%coupling

30%coupling

R Kodama et.al. Nature 412(2001)798 and 418(2002)933.Implosion

beams

0.5 PW laser

Gekko “Cone” implosion

The first cone coupled fast ignition experiment at the Gekko laser in Japan gave very encouraging results

• 0.5PW ignitor beam gave ≈ 20% energy coupling to imploded CD

• 1000x increased DD neutrons

Outstanding question for FI is What coupling is the efficiency at ignition scale ?

50 m

SP Laser

The energy required in the ignition hot spot and the optimum electron energy are well established

E

z

2r

DT

Fast Ignition region

T = 12keV, R = 0.6 g/cm2

Optimal ignition criteria:

E = 18kJ in <2MeV> electronsP = 0.9 PW => t = 20psI = 6.8x1019 W/cm2 => r = 20m

For = 300 g/cm3 assemblywe need to deliver to the fuel:

S. Atzeni, Phys. Plas. 8, 3316 (1999)

M Tabak et al Fus. Sci. Tech. (2006)

• Coupling efficiency depends on:– laser conversion to electrons– energy spectrum of electrons– collimation of electron transport – cone tip to dense plasma separation

€

Eign = 140ρ

100g /cm3

⎛

⎝ ⎜

⎞

⎠ ⎟

−1.85

kJ

Maximizing coupling efficiency at full scale is the overall design challenge in FI

Hybrid PIC coupled to hydro-modeling predicts the electron transport and electron coupling efficiency to the ignition spot

No B field 115 kJ

With B field 43 kJ300kJ drive 1D fuel

The focusing effect of azimuthal B from dB/dt= curl(E) increases transport efficiency by factor >2.5x

A A Solodov et al. ( preprint of publication )

Increased source divergence and distance to fuel increase the ignition energy - reduction by B field collimation is robust

Coupling of electron source to ignition hot spot can be > 50% efficient for typical beam divergence and transport distance

J Honrubia and J Meyer ter Vehn EPS Plasma Conf 2008

Cold target experiments at <1PW show typically 40o cone angle of electron transport

Al thickness micron

LULI

20J,0.5 ps

RAL

100J,0.8 ps

Cone angle 40o

Min radius 37 m

2500 5000 7500 10000 125000905xray03

180 m

Cu

20m

Al

20 m

0

100

200

300

400

500

600

0 100 200 300 400 500

Al thickness, µm

Spot diameter, µm RAL data

New warm plasma experiments are planned using long pulse beamsto prepare plasma ( A Mackinnon talk to follow )

40ocone

R Stephens et al. Phys Rev E,69, 066414, ( 2004)

Recent 2D PIC modeling predicts a cooler two temperature

electron source and 30 to 35% conversion to electrons

Chrisman , Sentoku and Kemp

PoP, 2008

Cool component is from light pressure steepened interface

and hot component from critical density shelf

Possibility of optimizing Thot and absorption efficiency

using low density foam layer to tailor the density profile

H Sakagami et al. FIW 2008A Kemp et al. PRL 2008

Coupling efficiency and effective Thot inferred from Ohmic potential limited transport in cone- wire targets at Vulcan PW

500 µm

1m 10 m

256 XUV

M Key et al Proc IFSA 2005 and J King et al PoP ( submitted)

•Sensitivity to pre-pulse and cone wall thicknessmeasured at Titan

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Electron source studies with the Titan laser also point to eletron temperature < ponderomotive potential

•Hybrid PIC modeling of K data gives conversion efficiency •Thot analysis using focal spot power fraction v intensity

• Bremsstrahlung data consistent with CSK PIC modeling

More in talk by R Stephens to follow

Point designs require simultaneous optimizing of many aspects of the hot electron generation, electron transport and hydrodynamics

Compressed fuel

Near 1-D isochoric implosions to minimize low density high

temperature hotspot at center

ConeMinimize transport distance from cone to fuel

Minimize high-Z cone material in fuel

Cone tip survival

clear path for laser

The cone tip hydro problem is very challenging at full scale because at fixed separation of tip and ignition spot the pressure is much higher relative to smaller scale e.g. Gekko experiment

40 m

90 m

298 m

25 kJ Omega Scale

1D target designs for direct-drive FI use massive wetted foam shells insensitive to fluid instability

R3g/cm2 R1.9g/cm2 R0.7g/cm2

<>300-500g/cm3

R. Betti and C. Zhou, Phys. Plasmas 12, 110702 (2005)

EL20kJ P25-34atm 1.3 V2•107cm/s

• Peak R is 0.26g/cm,2 the highest R to date on OMEGA• Empty shells would achieve R0.7g/cm2

C. Zhou, W. Theobald, R. Betti, P.B. Radha, V. Smalyuk, C.K.Li et al, PRL2008

CH implosions with low adiabat were tested on OMEGA

D2 or

D3He

0 5 10 15

measured

predicted

Secondary proton spectrum

Energy (MeV)

a.u

.

D-3He fusion proton energy loss measured the high R

NIF can drive full scale FI targets using 650kJ indirect drive and ID designs for CD and DT are being developed

Small hotspot r ~ 2 g/cm2

1235 µm

1070 µm

870 µm

1139 µm1087 µm

DT

Be

10-6g/cm3

DT

Be

den

sity

(g

/cm

3)

radiustime (ns)

Tra

d (

eV)

Be (0.9%) Cu

•Peak power: 70TW

•Pulse length: 32 ns

•Max blue energy: 650kJ

•Contrast ratio: 35:1

•Peak Trad = 210eV

Hydro tests with Be/CD targets on NIF

will begin in 2010

More in talk by D Clark to follow

Destruction of cone tip by hydro jet and entrainment of ablated high z cone in to fuel are important design issues

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Stoeckl C. et al., Phys. Plasmas 14 112702 (2007)

Nagatomo et al PoP 2007

CH tamped cone

Direct ignition by the main PW pulse ( super-penetration ) isan option being considered thro’ modeling and experiment

• 1D hydro- modeling has established the density profile

• PIC modeling has shown the main pulse penetrating beyond critical density with relativistic self focusing Y Sentoku et al . Fus Sci Tech,49,278,(2006)

• Excessive Thot is a problem which could be mitigated with a shorter wavelength

•Nc to >1 gcm-3 requires >200m penetration -not modeled

•Shorter wavelength would allow penetration closer to the ignition region

1mm

Nc/4Nc 1gcm-3

There is however no self consistent point design for ignition

• 2D PIC modeling has shown channel production up to critical density in a plasma of full FI scale.

• Lacks modeling to show channel extension by hole boring to bring the laser close enough to the ignition region (requires ~200 m hole boring to few gcm-3)

• The propagation of the main pulse in the channel has not been modeled

• Shorter wavelength makes channel to higher density

The original channeling and hole boring scheme using a pre-pulse is being studied in the Omega EP project

1019 Wcm-2 hole boring in 1 mm scale sub criticaL density plasma C Ren FIW (2006)

There is so far no point design for high gain

Ion fast ignition by protons or carbon ions offers alternatives

with some attractive features •Light pressure and BOA for C ions NEW

•TNSA for protons

J Honrubia EPS Plasma Conf 2008

M Key et al Fus Sci Tech 2006

J Fernandez et al. Proc IFSA 2007 and talk to follow

A conceptual design for proton fast ignition illustrates the issues

XUV

PW laser

Laser

Proton heating

Cu K image

m

Laser 100kJ,3 ps1020 Wcm-2

50kJ electrons kT=3 MeV

20 kJ protons kT= 3 MeV

•Radially uniform proton plasma jet required for smallest focal spot

•Proton source foil protects rear surface from pre-pulse -thickness limits conv. efficiency

•Cone maintains vacuum region for proton plasma jet formation and protects surface of proton source foil

•DT fuel at 500g/cc•60 m ignition spot(same as electron ignition)

•Scattering limits thickness of cone tip and separation from fuel

Requirements based on Ignitionwith protons :Atzeni et al .Nucl Fus 42,(2002)

Modeling of focusing suggests that FI requirements can be met with open geometry ( cone enclosed study ongoing )

Hybrid PIC modeling by M Foord LLNL using LSP code

80% of energy at >3MeV can be delivered to 60 m focal spot from an f/1 segment of a 300 m radius spherical shell

10 m Au,1m H , Thot 3 MeV , 47% conversion to protons >3MeV

Good electron to proton conversion efficiency with no depletion are predicted for thin Au targets with a hydride layer

Electron to Proton eff.

H 35%

ErH3 30%

Hybrid PIC modeling by M Foord LLNL using LSP code

0

10

20

30

40

Hydrides

BC

H LiH CHn

MgH2

CaH2

CsH ErH3

UH3

CH4

CH2

CH

HZ

ZHn

Thot=880keV5 + 1 m Au Å ZH

n

More in talk by M Foord to follow

Definitive integrated Fast Ignition experiments will be performed with facilities soon to come on line

Omega EP

PETAL

LIL

FIREX I NIF ARC Quad

NIF FI high gain

HIPER Firex II

Scheduled

Fall 2008 2009-2010 2009-2010 2011 ? ? ?

Long pulse(kJ)

25 60 10 800 800 200 50

Short pulse(kJ)

2.6 / beam 5.2 max

3.5 10 10 60 1w? 100 2w? 50

Scaled hydro R

0.2 ? 0.15 2 2 to 3 2 to 3 2 to 3

Density g/cc

300 ? 150 300-500 300-500 300-500 300-500

Hole boring

Y ? Y ?

Cone guided

Y Y Y Y Y Y Y

Near ignition

5keV Y

High gain >100 >100 >100

More in talks by W Theobald and A MacKinnon to follow

The high gain and low driver energy and possibility of two

opposed narrow cones of laser beams are attractive for IFE

Pure fusion and also fusion fission hybrids burning nuclear waste, are possible

I-LIFT (Japan), Hiper (Europe), LIFE (LLNL ) are examples

of study of FI power plant concepts

HED Science and IFE relevance of Fast Ignition ( FI )

•Fast ignition requires extremely high energy density 10keV, 300 to 500 g/cc in (40 m)3

•FI uses ignition methods (laser generated electron and ion beams)that can heat any material isochorically (using inertial confinement) to multi- keV temperature .

•Thermonuclear burn creates still higher energy densityFI cone targets will allow HED science using precise exposure of matter to extreme energy density and radiation and particle fluxes

•The underlying science of FI is that of more general HED science

•FI is an outstanding example of an application of HED science

•FI has significant advantages for an IFE power plant ( lower driver energy ,higher gain, better laser beam geometry )

•The potential and prospects of FI have led to major investments worldwide

Scientific challenges and opportunities

•Validated modeling and control of the source characteristics of laser generated relativistic electrons ( <E>=<2MeV>, >30% conversion ) at FI relevant laser parameters ( >1020 Wcm-2 , ~100kJ, <20 ps )

•Validated modeling and control of transport of electron energy to ignition spot - (magnetic collimation > 50% electron coupling efficiency )

•Advanced hydrodynamic design meeting multiple constraints for FI point designs e.g. optimizing implosion around a cone tip - designing targets for IFE with laser beams restricted to two cones

•Developing >10% efficient ion acceleration concepts to meet FI requirements ( e.g TNSA , light pressure and BOA concepts ) •Validated modeling and control of the focusing of laser generated ion beams to meet FI requirements ( 40 micron focal spot )

•Novel HED science using thermonuclear burn

Anticipated technical advances and opportunities

•Better integrated codes ( PIC, hybrid PIC, rad-hydro)- benchmarked by experiments - improved target point designs

•Next generation large scale integrated experiments using point designs ( Omega EP , FirexI , Petal and NIF ARC Quad )

•High gain FI using adapted or new laser facilities (adapted NIF or LMJ, Firex II , Hiper )

•HED science applications of FI thermonuclear burn

•IFE power plant concepts ( pure fusion and hybrid fission fusion )

•Laser technology for rep rated FI

•Low cost high volume target fabrication and injection •IFE demo and IFE power production