The role of symmetry in indirect-drive laser fusion

Hauer, A.; Suter, L. J.; Delamater, N. D.; Ress, David; Powers, L. V.; Magelssen, G. R.; Harris, David B.; Landen, O. L.; Lindmann, E.; Hsing, W. W.; Wilson, D. C.; Amendt, Peter; Thiessen, R.L.; Kopp, R. A.; Phillion, D. W.; Hammel, B. A.; Baker, D. A.; Wallace, Jessica; Turner, R. E.; Cray, M.; Watt, R. G.; Kilkenny, J. D.; Mack, J. M.

doi:10.1063/1.871210

Cited by 57 publications

(23 citation statements)

References 9 publications

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“…Thus, convergence is limited to a capsule x-ray emission radius of 50 μm with central ion temperatures in excess of T i = 30 million K as inferred from the D-D neutron time of flight spectrum. At these temperatures and densities, the capsule self-emission provides a sensitive measure of the hohlraum soft x-ray drive symmetry (26,27). Figure 3 shows that the capsule symmetry is controlled by the laser wavelength settings on the inner and outer cone of beams.…”

Section: Symmetric Inertial Confinement Fusion Implosions At Ultra-himentioning

confidence: 99%

Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies

Glenzer

MacGowan

Michel

et al. 2010

Science

331

184

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Indirect-drive hohlraum experiments at the National Ignition Facility have demonstrated symmetric capsule implosions at unprecedented laser drive energies of 0.7 MJ. 192 simultaneously fired laser beams heat ignition emulate hohlraums to radiation temperatures of 3.3 million Kelvin compressing 1.8-millimeter capsules by the soft x rays produced by the hohlraum. Self-generated plasma-optics gratings on either end of the hohlraum tune the laser power distribution in the hohlraum producing symmetric x-ray drive as inferred from the shape of the capsule self-emission. These experiments indicate conditions suitable for compressing deuterium-tritium filled capsules with the goal to achieve burning fusion plasmas and energy gain in the laboratory.With completion (1) and commissioning (2) of the National Ignition Facility (NIF) the quest for producing a burning fusion plasma has begun (3, 4). The goal of these experiments is to compress matter to densities and temperatures higher than the interior of the sun (5-7) which will initiate nuclear fusion and burn of hydrogen isotopes (8-10). This technique holds promise to demonstrate a highly efficient carbon-free process that will burn milligram quantities of nuclear fuel on each laser shot for producing energy gain in the laboratory.The NIF (11) consists of 192 laser beams that have been arranged into cones of beams to irradiate a target from the top and bottom hemispheres. This "indirect-drive" laser geometry has been chosen for the first experiments to heat the interior of centimeter-scale cylindrical gold hohlraums (8,(12)(13)(14)(15) through laser entrance holes (LEH) on the top and bottom end of the cylinder (Fig. 1). Hohlraums act as radiation enclosures that convert the optical laser light into soft x-rays that are characterized by the radiation temperature T RAD . Present ignition designs operate at temperatures of 270 to 305 eV or 3.1 to 3.5 million K. The radiation field compresses a spherical fusion capsule mounted in the center of the hohlraum by x-ray ablation of the outer shell. The ablation process compresses the cryogenically prepared solid deuterium-tritium fuel layer in a spherical rocket implosion. In the final stages, the fuel reaches densities 1000-times solid and the central hot spot temperatures will approach 100 million K to initiate the nuclear burn process.We have symmetrically imploded 1.8-mm diameter fusion capsules in cryogenically fielded centimeter-scale hohlraums at 20 K. These experiments show efficient hohlraum heating to radiation temperatures of 3.3 million K. In addition, the large scale-length plasmas encountered in these experiments have allowed us to use self-generated plasma optics gratings (16) to control the radiation symmetry (17) and to achieve symmetric fusion capsule implosions.Figure 2 A shows the laser power at the frequency-tripled wavelength of 351 nm versus time for two different pulse shapes. These 11-ns and 16-ns long pulses heat 8.4-mm long, 4.6-mm diameter hohlraums with 20% helium, 80% hydrogen (atomic) mixtures and ...

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Section: Symmetric Inertial Confinement Fusion Implosions At Ultra-himentioning

confidence: 99%

Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies

Glenzer

MacGowan

Michel

et al. 2010

Science

331

184

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“…Both temporally resolved (40 ps) data [5,19,22,30] from gated microchannelplate detectors [66] and absolutely calibrated time-integrated image plate data in four broad band x-ray energy channels have been measured. The equatorial measurements can be quantified [67][68][69] by decomposing the soft x-ray flux asymmetry at the capsule into Legendre polynomials, P n . Odd orders (n = 1, 3, ) are approximately zero due to the up-down illumination symmetry and low-order even modes (n = 2, 4) are the most important asymmetries.…”

Section: Implosion Symmetrymentioning

confidence: 99%

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

et al. 2012

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The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 mega joules produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 µm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 ± 3) µm, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 ± 0.09) g cm −2 result in fuel densities approaching 600 g cm −3 . The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 ± 0.1) keV that is measured with neutron time of flight spectra. Absolute neutron yields of (7.5 ± 0.1) × 10 14 have been recorded from the magnetic recoil spectrometer and nuclear activation diagnostics while gamma ray measurements provide the duration of nuclear activity of (170 ± 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date. This achievement is the result of the first hohlraum and capsule tuning experiments where the stagnation pressures have been systematically increased by more than a factor of 10 by fielding low-entropy implosions through the control of radiation symmetry, small hot electron production, and proper shock timing. The stagnation pressure is above 100 Gbar resulting in high Lawson confinement parameters of P τ 10 atm s. Comparisons with radiation-hydrodynamic simulations indicate that the pressure is within a factor of three required for reaching ignition and high yield. This will be the focus of future higher-velocity implosions that will employ additional optimizations of hohlraum, capsule and laser pulse shape conditions.

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“…Implosion symmetry experiments have demonstrated that P2 symmetry can be predicted and measured to -1'XOusing vacuum and low-Z-lined hohlraums. [6,7] Experiments on Nova have tested gas-filled hohlraum performance. In these experiments, whose conditions are described below, the plasma conditions are chosen to approximate part of the NW hohlraum conditions.…”

Section: Introductionmentioning

confidence: 99%

Improved gas-filled hohlraum performance on Nova with beam smoothing

et al. 1998

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FRGas-filled hohlraums are presently the base line ignition target design for the National Ignition Facility. Initial Nova experiments on gasfilled hohlraums showed that radiation temperature was reduced due to SBS and SRS scattering losses and that implosion symmetry had shifted compared with vacuum hohlraums and calculations. Subsequent single beam experiments imaging thermal x-ray emissionshowed the shift is due to laser-plasma heating dynamics and filarnentation in a flowing plasma. Experiments using a single beam have shown that scattering losses and effects of filamentation are reduced when the beam is smoothed with an random phase plate (RPP) or kinoform phase plate (KPP). Scattering is further reduced less than 5% of the incident laser energy when SSD is added.to

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The role of symmetry in indirect-drive laser fusion

Cited by 57 publications

References 9 publications

Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies

Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies

Cryogenic thermonuclear fuel implosions on the National Ignition Facility

Improved gas-filled hohlraum performance on Nova with beam smoothing

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