Direct-Drive Inertial Confinement Fusion Researchat the Laboratory for Laser Energetics:

Charting the Path to Thermonuclear Ignition

20th IAEA Fusion Energy ConferenceVilamoura, Portugal1–6 November 2004

R. L. McCrory, S. P. ReganUniversity of RochesterLaboratory for Laser Energetics

OMEGA30 kJ

60 beams

Relativesize

240 ft

National Ignition Facility (NIF)1.8 MJ

192 beams

NIFThe National Ignition Facility

Collaborators

S. J. Loucks, D. D. Meyerhofer, S. Skupsky, R. Betti, T. R. Boehly, R. S. Craxton,T. J. B. Collins, J. A. Delettrez, D. Edgell, R. Epstein, V. Yu. Glebov, V. N. Goncharov,D. R. Harding, R. L. Keck, J. P. Knauer, J. Marciante, J. A. Marozas, F. J. Marshall,

A. Maximov, P. W. McKenty, J. Myatt, P. B. Radha, T. C. Sangster, W. Seka,V. A. Smalyuk, J. M. Soures, C. Stoeckl, B. Yaakobi, and J. D. Zuegel

Laboratory for Laser Energetics, University of Rochester250 East River Road, Rochester, NY 14623-1299

C. K. Li, R. D. Petrasso, F. H. Séguin, and J. A. FrenjePlasma Science and Fusion Center, MIT

Boston, MA, USA

S. Paladino, C. Freeman, and K. FletcherState University of New York at Geneseo

Geneseo, NY, USA

Significant theoretical and experimental progresscontinues to be made at LLE – charting the pathto ignition with direct-drive ICF

I1565

• Ignition target designs are being validated on OMEGA withscaled implosions of cryogenic D2/DT targets.

• Symmetric direct drive on the National Ignition Facility (NIF)is predicted to achieve high-gain (~40).

• Direct drive targets are predicted to ignite on the NIF whileit is in x-ray-drive configuration with polar direct drive (PDD).

• Fully integrated fast-ignition (FI) experiments will begin onOMEGA with the completion of the high energy petawatt(HEPW) upgrade – OMEGA EP.

Summary

Prospects for thermonuclear ignition with directdrive on the NIF are extremely promising.

Outline

• Direct-drive inertial confinement fusion (ICF)

• OMEGA

• Symmetric illumination direct-drive ignition designs

• Polar direct drive

• Fast ignition research

Ablation is used to generate the extreme pressures requiredto compress a fusion capsule to ignition conditions

S5e

“Hot-spot” ignition requires the core temperature to be at least10 keV and the core fuel areal density to exceed ~300 mg/cm2.

2. Compression

Implodingpellet

Expandingblowoff

1. Irradiation

Laser orx ray DT fuel–filled

pellet

3. Thermonuclear ignition

T

4

8

0

12

Tem

per

atu

re (

keV

)

100

200

300

0

Den

sity

(g

/cm

3 )

0 200 400 600 800

ρ

Distance (µm)

20 40 60 70 80

ρR (mg/cm2)

Compressed pellet

TC2998w

• 60 beams• >30 kJ UV on target• 1%–2% irradiation nonuniformity• Flexible pulse shaping• Short shot cycle (1 h)

The OMEGA laser is the most powerful UVlaser for fusion research in the world

Laser bay

Target bay

I1517b

OMEGA creates extreme states of matterwith high reproducibility

• Compressed pressures of 5~10 Gbar

• DT neutron yields of 1014

• Peak ion temperatures of ~20 keV

Benchmark direct-drive implosions

15-atmD2~450 µm

CH (~20 µm)

EL ~ 23 kJτ = 1 ns square

1011

2000 2001 2002 2003 2004 2005Year

Pri

mar

y n

eutr

on

yie

ld

1010

OMEGA cryogenic targets are energy scaledfrom the NIF symmetric direct-drive point design

E11251j

Energy ~ radius3;power ~ radius2;

time ~ radius

Initial cryogenic DT implosions are expected in spring 2005.

Gain (1-D) = 45

1.69 mm

~3 µm CHNIF: 1.5 MJ

1.35 mm

DT ice

DT gas

~4 µm CH

0.36 mm

0.46 mm

OMEGA: 30 kJ

D2 ice

D2gas

103

102

101

100

0 2 4 6 8 1010–1

NIFα ~ 3

OMEGAα ~ 4

α =Pfuel

PFermi

Time (ns)

Po

wer

(T

W)

E12130c

Perturbation seeds from four sources early in the implosiondetermine the final capsule performance

Early time

Acceleration phaseDeceleration phase

Peak compression

Rayleigh–Taylor growthand feedthrough

Diagnostics• Neutronics• Charge particle spectroscopy• X-ray spectroscopy

Main laser drive

Rayleigh–Taylor andBell–Plesset growth

DT gas

Fusion burn/ ignition

Hot-spot formation

Shell mix

DT ice

Laser imprint 1

Laser drive symmetry 4

Absorption/coupling

HSFeedout perturbations

Surface roughness 2Inner surface3

DT-ice

rm

s

TC5577e

A global nonuniformity budget for the direct-drive pointdesign can be formed by scaling gain with σ

* P. McKenty et al., Phys. Plasmas 8, 2315 (2001).Multiplier

Applied SSD bandwidth (laser imprint)(two-color cycle × 1 THz)

On-target power imbalance (× 2% rms)

Inner-surface roughness (× 1-µm rms)

Outer-surface roughness (× 80 nm)

• The NIF gain* and OMEGA yield can be related by

σ2 = 0.06 σ2 + σ2�<10 ��10 ;

σ� = rms amplitudes at the end of the acc. phase.

σ (µ

m)

0.0 1.51.00.5 2.00

1

2

Current NIFspecifications

DD point designperformance

40

20

00 1 2

σ (µm)

TN

gai

n

TC5950c

Shell stability and compressibilitydepend on the adiabat

• Mimimum energy required for ignition:1,2 Emin ~ α1.88 α = P/PFermi

• Rayleigh–Taylor instability growth γ = αRT(kg)1/2 – βRTkVa Va ~ α3/5

0.00 0.01 0.02 0.03

2

4

6

8

10

12

14Density × 5

AdiabatAblated mass

0

Into Va

Into Emin

Mass (mg)

Main fuel layer

Adiabat shaping is achieved usinga high intensity picket laser pulse.

Laser imprint

1M. Herrmann et al., Phys. Plasmas 8, 2296 (2001).2R. Betti et al., Phys. Plasmas 9, 2277 (2000).

E12854a

Measured radiographs show significantimprint reduction with picket pulses

V. N. Goncharov, Phys. Plasmas 10, 1906 (2003).

120 µm 60 µm 30 µm

2-D DPP’s with singlewavelength modulations at:

0 2 4Time (ns)

0

2

4

6

8

Inte

nsi

ty(W

/cm

2 ×

1014

)

• Measurements at 100 µm distance traveled.

CH Foam0.18 g/cc

5 µm 100 µm

Laser

E12855b

Optical-depth modulations are significantly reducedat shorter wavelengths using a picket pulse

1.00

0.10

0.01

Am

plit

ud

e (O

D)

120 µm 60 µm 30 µm

1.5 2.5 3.0 3.5 1.5 3.5

Time (ns)

1.5 3.5

Wavelength

No picket

Picket

No picket

Picket

No picket

Picket

Time (ns)

Wavelength

Time (ns)

Wavelength

2.0 2.5 3.02.0 2.5 3.02.0

TC6341b

Adiabat shaping is a very powerful techniqueto reduce the growth of hydrodynamic instabilities

α = 220

15

10

5

00 1 2 3

Po

wer

(T

W)

Time (ns)

5 µm80 µm

345 µm

D2 gasD2 ice

CH

R (

µm)

4.20

0.10

ρ (g/cc)

Z (µm)

290

25010060

Picket

200

300

100

00 100 200 300

200

300

100

0

290

25010060

No picket

R (

µm)

σ = 1.12 µm

σ > 10 µm

Imprint simulationsORCHID: � = 2–200, DPP + PS, 1-THz SSD

TC6339d

Direct-drive target stability is dramaticallyimproved when adiabat shaping is applied

The benefit of pickets has been confirmed in NRLand LLNL simulations.

Multiplier

2

1

00.0 0.5 1.0 1.5 2.0

σ (µ

m)

Current NIFspecification

Withpicket

0 1 2G

ain

σ (µm)

40

20

0

Laser imprintPower imbalanceIce roughnessOuter-surface roughness

I1566

Reduction of the on-target laser irradiation nonuniformityon OMEGA dramatically improved implosion performance

10–2

10–1

100

0 10 20 30 40 50

Spherical harmonic � mode

σ RM

S (

%)

Calculated on-targetnonuniformity levels

SG3 irradiation σRMS = 1.43%

SG4 irradiation σRMS = 0.79%

• Far field intensity envelope: I(r) ∝ exp

• New phase plate design n = 4.1 (SG4)

• Old phase plate design n = 2.2 (SG3)

–rδ

⎛⎝

⎞⎠n⎡

⎣⎢

⎤

⎦⎥

SG4 irradiationSG3 irradiation

D2(3)CH[24]

1.0

0.8

0.6

0.4

0.2

0.0YO

C [Y

1n(e

xpt.

)/Y

1n(1

-D)]

Calculated convergence ratio

20 25 30 35 40 45

D2(3)CH[27]

D2(3)CH[20]

YOC

Dominated bylaser imprint

Sensitive tolow �-modeirradiation

nonuniformity

Power Imbalance

T1905e

Submicron rms ice layers were demonstrated; the smoothestlayers were confined to localized regions of the target

• 24 views every 15° in “x” and “y”• 0.8 to 1.4 µm over 1/4 of target’s surface

390

370

350

330

310

2900 100 200 300

Unwrapped Image

Angle (°)

Rad

ius

(pix

els)

2.5

1.0

1.5

2.0

Cryo target 2035-291 φ = 165

600 1000200

200

600

1000

800

400

Y (

pix

els)

X (pixels)

0

102101100

Mode �

10–6

10–4

10–2

100

Sp

ectr

um

(µm

2 )

Inner 0.8-µm rmsOuter 0.3-µm rms

Shadowgraph of layeredcryogenic target

Ice Roughness

2-D DRACO demonstrates good agreement in predictingtarget performance for shot 35713 (α ~ 4)

TC6465d

100

75

0

R (

µm)

50250–25–50Z (µm)

DRACO 2-D densitynear peak burn,shot 35713α ~ 4, 17.5 kJ

Expt 1-D 2-D

Y1n 1.61 × 1010 9.90 × 1010 1.81 × 1010

Y2n 2.55 × 108 1.70 × 109 2.78 × 108

<ρR> (mg/cm2) 88 117 133

Tion (keV) 3.0 1.9 1.70

53

24

5

Density(g/cm3)

11

50

25

Mode �

100 101 102S

pec

tru

m (

µm2 ) Inner 3.91-µm rms

101

100

10–1

10–2

10–3

10–4

OMEGA Implosions

E12008k

A stability analysis* of the α = 4 design defines the ignition-scaling performance window for cryogenic implosions

*P. McKenty et al., Phys. Plasma 11, 2790 (2004).

• The NIF gain and OMEGA yield can be related by

σ2 = 0.06σ�<102 + σ�≥10

2 ,where the σ�’s are the rms amplitudes at the end of the acceleration phase*.

NIF (α = 3)

1.2

1.0

0.8

0.6

0.4

0.2

0.0 0.5 1.0 1.5 2.0 2.5 3.0

σ (µm)

No

rmal

ized

yie

ld

0.0

OMEGA(α = 4)

1-THz, 2-D SSD with PS,1-µm-rms ice roughness,840- outer-surface roughness,1% rms power imbalance

103

Targ

et g

ain

100

101

102

α = 1

2

3

4

1.0 1.2 1.4 1.6 1.8 2.0

Incident laser energy (MJ)

(α = 6)

DRACO results

E13085d

Hydrodynamic simulations are consistent with implosiondata over a wide range of ice roughness and target offset

0.8

0.6

0.4

0.2

0.0

YO

C

33687(42 µm)

α ~ 6

0 543

rms ice roughness (µm)modes � = 1 to 16

21

30-µmoffset

33600(28 µm)

35653(38 µm)

Performance with NIF requirements

34999(32 µm)

34998(28 µm)

34945(30 µm)

0.6

0.4

0.2

0.0

α ~ 4

0 543

rms ice roughness (µm)modes � = 1 to 16

21

DRACO (no offset)

Performance with NIF requirements

25-µmoffset

DRACO (no offset)

35652(18 µm)

35713(15 µm)

TC6631a

Direct drive can achieve ignition while the NIFis in the x-ray-drive configuration

Standard pointingwith x-ray-driveconfiguration Repointing for PDD

23.5°30°

45, 50°

40°23.5°

75°50°30°23.5°

23.5°30°

45, 50°

Gain = 10

0 25 50 75 100

250

500

0

ρ (g/cc)

z (µm)

2-D hydrodynamic simulations

• Polar direct drive (PDD) is based onthe optimization of phase-plate design,beam pointing, and pulse shaping.

Polar Direct Drive

Ti = 10 keVTi = 4 keV

Ti = 12 keV

Ti = 6 keV

E13488

2-D hydrocode simulations track the measured targetnonuniformity for initial PDD experiments on OMEGA

• The NIF PDD configuration with 48 quads has been approximatedby repointing 40 beams for implosions on OMEGA

300

250

200

150

100

Expt.(1.25 ns)

SAGE (7 µm rms)

Sh

ell r

adiu

s (µ

m)

1801501209060300Polar angle θ (°)

SAGE (9 µm rms)

Expt.(1.5 ns)OMEGA beam

NIF ID quad

E12526b

A complementary approach to hot-spot ignition, namelyfast ignition is an active area of research at LLE

(a) (b)

Fast Ignition

Fast IgnitorConventional ICF

Fastinjectionof heat

Fast-heated side spot ignitesa high-density fuel ballρhot ≈ ρcold (isochoric)

Low-density central spot ignitesa high-density cold shellρThot ≈ ρTcold (isobaric)

T

r

ρT

r

ρ

E12527b

Ignition could be acheived at lower driveenergies with fast ignition

100

10

10.1 1.0 10

Targ

et g

ain

Driver energy (MJ)

Fast ignition

v v =4x107

NIF pointdesigns

1000-MJ yieldNIF

Indirectdrive

Direct drive

300 g/cc,92 kJ,4 × 1019

150 g/cc,330 kJ,1.8 × 1019

100-MJ yield

10-MJ yield

v =4×107

200g/cc,200kJ,2.5 × 1019

Direct-drive FI at the NIF

v v =3x107 v =3×107

The two viable fast-ignition concepts share fundamentalissues: hot-electron production and transport to the core

E11710e

Holeboring Ignition

2.6 kJ, 10 psLight pressurebores hole in

coronal plasma. ~1-MeV electronsheat DT fuel to~10 keV, ~300 g/cc.

Channeling concept Cone-focused concept

Au cone

Single ignitorbeam: 2.6 kJ

in 10 ps

e–

OMEGALaser Bay

OMEGAtarget chamber

OMEGA EPLaser Bay

Compressionchamber

G5546p

Fast ignition with cryogenic fuel will be conductedon OMEGA with the high energy petawatt OMEGA EP

OMEGA EP

Short-pulseperformance

Short pulse (IR)

IR energyon-target (kJ)

Intensity (W/cm2)

Short-pulsebeam 1

1 to 100 ps

2.6

6 × 1020

Short-pulsebeam 2

35 to 100 ps

2.6

~ 4 × 1018

OMEGA EPtargetchamber

Mainamplifiers

OMEGA EP will becompleted in FY07

Significant theoretical and experimental progresscontinues to be made at LLE – charting the pathto ignition with direct-drive ICF

I1565

• Ignition target designs are being validated on OMEGA withscaled implosions of cryogenic D2/DT targets.

• Symmetric direct drive on the National Ignition Facility (NIF)is predicted to achieve high-gain (~40).

• Direct drive targets are predicted to ignite on the NIF whileit is in x-ray-drive configuration with polar direct drive (PDD).

• Fully integrated fast-ignition (FI) experiments will begin onOMEGA with the completion of the high energy petawatt(HEPW) upgrade – OMEGA EP.

Prospects for thermonuclear ignition with directdrive on the NIF are extremely promising.

Summary/Conclusions

E12573b

Gas-tight fast-ignition targets were developedfor fuel-assembly experiments

• 870-µm OD shell

• 24-µm wall

• ~10 atm D2 or D3He fill

• 35° half-angle gold cone

• Backlighting– 35 beams, 12 kJ, 1 ns on target– 15 beams, 6 kJ, 1 ns on backlighter

• Areal-density measurements– 55 beams, 22 kJ, 1 ns on target

870 µm

E12558d

The backlit framing-camera images show the coreassembly and cone reaction in great detail

1.73 ns 1.85 ns 2.04 ns 2.15 ns

2.23 ns 2.54 ns 2.65 ns 2.77 ns

Shot 32381, V backlighter,D2 fill, yield = 6 × 106,

ρR ~ 60 mg/cm2 (D3He proton dE/dx)

200 µm

Cone

Shell