Performance of and Initial Results from the OMEGA EP Laser System

Performance of and Initial Results from the OMEGA EP Laser System Initial Integrated Fast-Ignition Results

Neutron yield (×107)

4

Integrated FI shots Average OMEGA only

3 2 1 0

3.5

3.6

3.7

OMEGA EP time (ns)

D. D. Meyerhofer University of Rochester Laboratory for Laser Energetics

Inertial Fusion Sciences and Applications San Francisco, CA 6–11 September 2009

Summary

OMEGA EP is routinely delivering the highest energy short-pulse beam in the world

• The performance of the OMEGA EP high-energy petawatt laser system continues to improve—OMEGA EP was completed in April 2008 • New laser and target diagnostics are continually being added – 83 target diagnostics qualified – single-shot contrast diagnostics will be installed in the next few months • Many users have obtained good initial results • Experiments have found that the laser-to-fast-electron coupling is independent of energy, to 1 kJ, and pulse duration, to 10 ps • Initial Fast-Ignition (FI) experiments have doubled the neutron yield of a cone-in-shell implosion with a 1-kJ, 10-ps FI beam An OMEGA EP beam fired 2.1 kJ on target in a 15-ps pulse last week. E18226

Collaborators

R. Betti, T. R. Boehly, J. Bromage, C. Dorrer, V. Yu. Glebov, J. H. Kelly, B. E. Kruschwitz, S. J. Loucks, R. L. McCrory, S. F. B. Morse, J. F. Myatt, P. M. Nilson, J. Qiao, T. C. Sangster, A. A. Solodov, C. Stoeckl, W. Theobald, and J. D. Zuegel Laboratory for Laser Energetics University of Rochester

OMEGA EP includes high-energy petawatt capability at 1-nm wavelength OMEGA target chamber OMEGA EP target chamber Main amplifiers

OMEGAay Laser B Compressor chamber

4 Beam 1 2 3

Booster amplifiers OMEGA EP Laser Bay

Performance Capabilities Wavelength Pulse width Energy on target (kJ) Intensity (W/cm2) Focusing (diam)

G6957x

Short-Pulse Beam Infrared (1.0 nm) 1 to 100 ps 2.6 kJ, 10–100 ps grating limited 80% in 20 nm

Short-pulse beams can be directed either to OMEGA or to the OMEGA EP target chamber.

The FY10 short-pulse operating envelope is constrained by optics damage and the B-integral of the disposable debris shield (DDS) Ultimate no DDS Ultimate with DDS FY10 no DDS FY10 with DDS

3000

Energy on target

2500

Sept. 2009

2000 1500 1000

1000 J

500 85 J

0

12 ps

850 J

1

Operating regime with DDS FY10

10

100

Pulse width (ps)

G8476c

A test energy ramp in September 2009 will assess expanded operational envelope—2.1 kJ on target to date.

The OMEGA EP focal spot continues to improve with R80 < 25 nm demonstrated

0.8

R80 = 22.7 nm 100

0.6 y (nm)

Encircled energy (normal)

1.0

0.4 0.2 0.0

On-target intensity

20

–1

0

–2

–50

–3

40

50 100 0 x (nm)

60

Radius (nm) G8730c

0

50

–100 –100 –50

0

log

80

BL1 to OMEGA EP sidelighter indicated, shot 4800

–4

100

A single-shot, third-order cross-correlator based on an optical pulse replicator has been developed* 3~ HR

Filters

Detection plane Signal (3~) 2~ pulse

Lens

THG crystal 1~ pulse under test

2~ HR 2~ PR Density filters

Optical pulse replicator Spatial attenuation stage

Pulse replicator output (2~)

1~ HR

• 1~ pulse intensity is obtained by nonlinear interaction with a sequence of 2~ sampling pulses generated by a pulse replicator. • Sensitivity adjusted for different temporal ranges using neutral density filters after the pulse replicator. • Background-free detection at 3~ for high-dynamic-range (80 to 100 dB) measurements. This cross-correlator will be a routine OMEGA EP diagnostic in a few months. E16459b

*C. Dorrer, Opt. Express 16, 13534 (2008).

The results from a number of OMEGA EP experiments will be presented at this meeting O.1.3.4

H.-S. Park

Results from Rayleigh–Taylor experiments using OMEGA and OMEGA EP – including development of 20-keV backlighting capability

P.1.10.002

M. Primout

Recent progress and prospects in multi-keV/ns to multi-MeV/ps x-ray sources at OMEGA

P.2.10.033

H. Chen

Escaping hot-electron measurements from small to large short-pulse laser facilities

P.3.10.026

K. Flippo

First observations of energetic laseraccelerated ions from the OMEGA EP laser with 1000 J in 10 ps

P.3.10.054

H. Sawada

Investigation of fast-electron transport in solid and shock-heated targets

P.3.10.059

L. Willingale OMEGA EP laser propagation through near-critical density plasma

In its first year, OMEGA EP has produced exciting physics results. E18228

Fast-electron recirculation in mass-limited targets allows access to high-energy-density phenomena PBR K a Bremsstrahlung

Kb K-photon production

• Majority of fast electrons are stopped in the target

20 to 1019 W/cm2 500 nm

Debye sheaths uE q á 1012 V/m

2 to 20 nm

Fastest electrons escape 1S.

• Provides a simple geometry for testing laser-coupling, electron-generation, and target-heating models3,4

P. Hatchett et al., Phys. Plasmas 7, 2076 (2000). Snavely et al., Phys. Rev. Lett. 85, 2945 (2000). 3W. Theobald et al., Phys. Plasmas 13, 043102 (2006). 4J. Myatt et al., Phys. Plasmas 14, 056301 (2007).

2R. A. E16142f

• Refluxing is caused by Debye-sheath field effects1,2

K-photon radiation reveals hot-electron production and bulk heating of small-mass targets*

N

Ionization

M

Depleted population

L Ka (L8.05 keV)

Kb (L8.91 keV)

K Copper energy levels

E16143f

• Intense laser–plasma interaction produces energetic electrons that leave K-shell vacancies • Ka yield indicates hot-electron conversion efficiency • Inelastic collisions heat the target and ionize outer shell electrons • Collisional ionization with thermal background plasma occurs • Te > 100 eV causes significant M-shell depletion, which affects Kb yield • Target heating is inferred from Kb/Ka

*J. Myatt et al., Phys. Plasmas 14, 056301 (2007). *G. Gregori et al., Contrib. Plasma Phys. 45, 284 (2005).

K-photon emission-suppression measurements were performed on OMEGA EP using up to 1.3-kJ, 10-ps pulses

• The laser-energy conversion efficiency into fast electrons is independent of the laser pulse duration (xP ≤ 10 ps)

1.2 Normalized Kb/Ka

• Similar K-photon emission characteristics are observed using 1-ps MTW pulses and 10-ps OMEGA EP pulses

1.0

hL→e = ~20% 0

100

0.8 0.6

150

0.4

200

0.2

400 0.0 7 6 5 4 3 2 10 10 10 10 10 10 Laser energy (J)/ target volume (mm3)

Weighted temperature (eV)

MTW: EL = 1 J, xL = 1 ps OMEGA EP: EL ≤ 1300 J, xL = 10 ps

Increasing energy density

The inferred laser-to-hot-electron conversion efficiency is ~20% and constant for 1-J, 1-ps to 1.3-kJ, 10-ps laser pulses. E17611d

P. M. Nilson et al., Phys. Rev. E 79, 016406 (2009). P. M. Nilson et al., Phys. Plasmas 15, 056308 (2008). P. M. Nilson, submitted to Phys. Rev. Lett. (2009).

Integrated fast-ignition experiments have begun on the Omega Laser Facility • LLE has begun integrated cone-in-shell fast-ignition experiments with warm CD shells Re-entrant cone HEPW laser

CD shell

MeV electrons Imploded fuel Shock wave

• Initial experiments showed an increase in x-ray emission for the cone tip, but x-ray and c background blinded neutron diagnostics • A new liquid scintillator detector was developed that makes it possible to measure neutron yield with the OMEGA EP laser beam* • Approximately 1 kJ of a 10-ps OMEGA EP laser pulse was incident on a compressed target E18169a

*See Sangster O.5.6.3

A neutron time-of-flight detector with a liquid scintillator showed no long decay tail from an intense hard x-ray pulse FSC Gold cone, 10-ps, 1-kJ OMEGA EP beam

Signal (V)

0.2 0.0 –0.2

Plastic scintillator

Gate end

–0.4

Shot 53527

Signal (V)

–0.6 0.0 –0.2

Gate end

–0.4

D2 neutron signal Shot 54411

0

200

600 400 Time (ns)

800

Liquid scintillator with O2 saturated Xylene

1000

This scintillator is used in FI experiments to measure the D2 neutron yield. E18058b

See Sangster O.5.6.3

0.010

Measurements limited by neutron statistics ~12 neutrons

0.000 –0.010 –0.020 –0.030

Initial integrated fast-ignition results with 1-kJ, 10-ps OMEGA EP beam

3.55 ns

560 580 600 620 640 Time (ns)

Neutron yield (×107)

Neutron detector signal (V)

The neutron yield increased a factor of two with an appropriately timed OMEGA EP beam

4 3 2 1 0

Integrated FI shots Average OMEGA only

3.5

3.6

3.7

OMEGA EP arrival time (ns)

~1.5 × 107 additional neutrons were produced with the FI beam. E18171a

• DRACO2 is a 2-D cylindrically symmetric hydrodynamic code that includes the necessary physics for ignition and burn of the imploded capsules • LSP3 is a 2-D/3-D implicit-hybrid PIC code • Simulations show good agreement with the measured neutron yields with 1 kJ of OMEGA EP laser energy with 10% laser fast-electron conversion efficiency

E18227

Neutron-yield increase

An integrated fast-ignition simulation1 capability combining the hydrocode DRACO2 with the particle code LSP3 reproduces the experimental results FSC Neutron yield: Sim. versus Exp.

1010

Sim., 20-nm spot, 10 ps, h = 30%

109

Sim., 40-nm spot, h = 20%

108 107

Experiment, 1 kJ, 10 ps

0

Sim., 40-nm spot, 10 ps, h = 20%

Simulation,1 kJ, 10 ps, 40-nm spot, h . 10%

2 1 Laser-pulse energy (kJ)

3

1A. Solodov et al., Phys. Plasmas 15, 112702 (2008); ibid. 16, 056309 (2009). 2P. B. Radha et al., Phys. Plasmas 12, 056307 (2005). 3D. R. Welch et al., Phys. Plasmas 13, 063105 (2006).

Summary/Conclusions

OMEGA EP is routinely delivering the highest energy short-pulse beam in the world

• The performance of the OMEGA EP high-energy petawatt laser system continues to improve—OMEGA EP was completed in April 2008 • New laser and target diagnostics are continually being added – 83 target diagnostics qualified – single-shot contrast diagnostics will be installed in the next few months • Many users have obtained good initial results • Experiments have found that the laser-to-fast-electron coupling is independent of energy, to 1 kJ, and pulse duration, to 10 ps • Initial Fast-Ignition (FI) experiments have doubled the neutron yield of a cone-in-shell implosion with a 1-kJ, 10-ps FI beam An OMEGA EP beam fired 2.1 kJ on target in a 15-ps pulse last week. E18226