Analyses of laser-plasma interactions in National Ignition Facility ignition targets

Hinkel, D. E.; Callahan, D. A.; Langdon, A. B.; Langer, S.; Still, C. H.; Williams, E. A.

doi:10.1063/1.2901127

Cited by 51 publications

(36 citation statements)

References 27 publications

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“…Since no SRS was measured on the outer cones (nor predicted in our simulations -cf. [22]), and that the 30 • cone measured a constant backscatter loss as we tuned ∆λ, we attributed the additional SRS to the undiagnosed 23.5 • cone.…”

Section: Inferring Srs On the 235 • Conementioning

confidence: 99%

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Michel¹,

Divol²,

Town³

et al. 2011

Phys. Rev. E

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By using three tunable wavelengths on different cones of laser beams on the National Ignition Facility, numerical simulations show that the energy transfer between beams can be tuned to redistribute the energy within the cones of beams most prone to backscatter instabilities. These radiative hydrodynamics and laser-plasma interaction simulations have been tested against large scale hohlraum experiments with two tunable wavelengths, and reproduce the hohlraum energetics and symmetry. Using a third wavelength provides a greater level of control of the laser energy distribution and coupling in the hohlraum, and could significantly reduce stimulated Raman scattering losses and increase the hohlraum radiation drive while maintaining a good implosion symmetry.

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Section: Inferring Srs On the 235 • Conementioning

confidence: 99%

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Michel¹,

Divol²,

Town³

et al. 2011

Phys. Rev. E

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“…The gain exponents for backscatter from individual quads originating in the interior of the hohlraum are calculated using the LIP post-processor. 8 We assume that the backscatter light backtracks the path of the incident light in each quad, and calculate the coupling of the backscattered light as it exits the hohlraum to each of the incoming intersecting quads via a separate Langmuir wave for each pump as shown schematically in Figure 11. The coupling uses a linear kinetic model and is estimated in the 1D limit but for a full 3D geometry, 37 in a very similar way to the model described in Ref.…”

Section: Application Of the Multi-pump Amplification Models To Obsmentioning

confidence: 99%

“…15), and estimates were made of the wavelengths and magnitudes of the scattering produced by the individual quads of beams. 8 Next, the region in which the quads intersect was analyzed to determine the amplification factors the light would experience as it left the target with the specified plasma conditions, and with the range of wavelengths and propagation directions of the scatter from individual beams in the interior. The gain exponents for backscatter from individual quads originating in the interior of the hohlraum are calculated using the LIP post-processor.…”

Section: Application Of the Multi-pump Amplification Models To Obsmentioning

confidence: 99%

“…1.3 MJ of 351 nm light in 192 beams with shaped power waveforms, incident in cones with four different angles on targets designed to produce fusion ignition by indirect drive. The construction of NIF and the need for accurate modeling of coupling to the targets, motivated extensive experimentally benchmarked modeling of the scattering of individual beams 8,9 because of its potential to limit the coupling of energy to the ignition targets.…”

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Multi-beam effects on backscatter and its saturation in experiments with conditions relevant to ignition

et al. 2011

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To optimize the coupling to indirect drive targets in the National Ignition Campaign (NIC) at the National Ignition Facility [E. Moses et al., Phys. Plasmas 16, 041006 (2009)], a model of stimulated scattering produced by multiple laser beams is used. The model has shown that scatter of the 351 nm beams can be significantly enhanced over single beam predictions in ignition relevant targets by the interaction of the multiple crossing beams with a millimeter scale length, 2.5 keV, 0.02−0.05 × critical density, plasma. The model uses a suite of simulation capabilities and its key aspects are benchmarked with experiments at smaller laser facilities. The model has also influenced the design of the initial targets used for NIC by showing that both the stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) can be reduced by the reduction of the plasma density in the beam intersection volume that is caused by an increase in the diameter of the laser entrance hole (LEH). In this model, a linear wave response leads to a small gain exponent produced by each crossing quad of beams (<∼1 per quad) which amplifies the scattering that originates in the target interior where the individual beams are separated and crosses many or all other beams near the LEH as it exits the target. As a result all 23 crossing quads of beams produce a total gain exponent of several or greater for seeds of light with wavelengths in the range that is expected for scattering from the interior (480 to 580 nm for SRS). This means that in the absence of wave saturation, the overall multi-beam scatter will be significantly larger than the expectations for single beams. The potential for non-linear saturation of the Langmuir waves amplifying SRS light is also analyzed with a two dimensional, vectorized, particle in cell code (2D VPIC) that is benchmarked by amplification experiments in a plasma with normalized parameters similar to ignition targets. The physics of cumulative scattering by multiple crossing beams that simultaneously amplify the same SBS light wave is further demonstrated in experiments that benchmark the linear models for the ion waves amplifying SBS. The expectation from this model and its experimental benchmarks is shown to be consistent with observations of stimulated Raman scatter in the first series of energetic experiments with ignition targets, confirming the importance of the multi-beam scattering model for optimizing coupling.

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“…In case that SRS is Landau damped (for high electron temperatures) or excluded (for over quarter-critical densities), SBS can become the dominant scattering mechanism. In the parameter regime relevant to the current design of indirect ICF, SRS is dominant for the inner beams while SBS is dominant for the outer beams [3,4]. When counter propagating beams cross, PB depends on the relative polarization between the beams [5].…”

Section: Introductionmentioning

confidence: 99%

Reducing parametric backscattering by polarization rotation

Barth

Fisch

2016

Physics of Plasmas

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When a laser passes through underdense plasmas, Raman and Brillouin Backscattering can reflect a substantial portion of the incident laser energy. This is a major loss mechanism, for example, in employing lasers in inertial confinement fusion. However, by slow rotation of the incident linear polarization, the overall reflectivity can be reduced significantly. Particle in cell simulations show that, for parameters similar to those of indirect drive fusion experiments, polarization rotation reduces the reflectivity by a factor of 5. A general, fluid-model based, analytical estimation for the reflectivity reduction agrees with simulations. However, in identifying the source of the backscatter reduction, it is difficult to disentangle the rotating polarization from the frequency separation based approach used to engineer the beam's polarization. Although the backscatter reduction arises similarly to other approaches that employ frequency separation, in the case here, the intensity remains constant in time.

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Analyses of laser-plasma interactions in National Ignition Facility ignition targets

Cited by 51 publications

References 27 publications

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Three-wavelength scheme to optimize hohlraum coupling on the National Ignition Facility

Multi-beam effects on backscatter and its saturation in experiments with conditions relevant to ignition

Reducing parametric backscattering by polarization rotation

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