Effects of ion trapping on crossed-laser-beam stimulated Brillouin scattering

Williams, E. A.; Cohen, B. I.; Divol, L.; Dorr, M.; Hittinger, Jeffrey; Hinkel, D. E.; Langdon, A. B.; Kirkwood, R. K.; Froula, D. H.; Glenzer, S. H.

doi:10.1063/1.1630573

Cited by 93 publications

(93 citation statements)

References 45 publications

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“…13 The demonstration of a strong wavelength dependence of seeded SBS forward scatter, or power transfer between crossing beams as it is now called, led to the concept of wavelength tuning of beams that enter ignition target at different angles 13 in order to control forward scatter and produce the laser power deposition profile needed on the interior of the hohlraum wall for symmetric implosions. As a result NIF now has wavelength tuning capability, 14 and an analysis of the SBS amplification of the forward going power of all entering beams by all other beams has been implemented and used to estimate the optimal wavelengths for the beams to produce symmetric x-ray drive in all ignition target designs. This analysis has also shown that frequency tuning can even correct the power deposition profile to compensate for other effects that distort the x-ray drive in the target.…”

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confidence: 99%

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

et al. 2011

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“…Analytical and numerical results were obtained for the steady-state crossbeam amplification with the ion wave damping rate a specified parameter. 11 The analysis shows that finite auto-resonant or anti-auto-resonant effects can be expected when the magnitude of the ion trapping nonlinear frequency shift is competitive with the ion wave damping rate, and these effects are stronger the larger the linear convective amplification is (see Fig. 4 …”

Section: Gradientmentioning

confidence: 99%

“…Williams, et al 11 considered auto-resonant enhancement and anti-auto-resonant decrease in the stimulated Brillouin scattering driven cross-beam interaction (where two incident lasers optically mix in the plasma flow and produce a beat-wave that resonantly excites an ion wave at the Doppler-shifted beat frequency and beat wavenumber of the two lasers). Analytical and numerical results were obtained for the steady-state crossbeam amplification with the ion wave damping rate a specified parameter.…”

Section: Gradientmentioning

confidence: 99%

“…Earlier work on the theory and simulation of SBS has shown the importance of wave breaking and ion trapping, [1][2][3][4][6][7][8][9][10][11][12] harmonic generation, [13][14][15] and secondary instability of the ion wave. [1][2][3][4][5] In 1D simulations of SBBS, the inclusion of kinetic electrons has made a difference in the saturation of SBBS.…”

Section: Introductionmentioning

confidence: 99%

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Effects of ion-ion collisions and inhomogeneity in two-dimensional kinetic ion simulations of stimulated Brillouin backscattering

et al. 2006

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Langdon, and E.A. Williams, Phys. Plasmas 4, 956 (1997)] hybrid code (kinetic particle ions and Boltzmann fluid electrons) have been used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability including the effects of ion-ion collisions and inhomogeneity. Ion-ion collisions tend to increase ion-wave dissipation, which decreases the gain exponent for stimulated Brillouin backscattering; and the peak Brillouin backscatter reflectivities tend to decrease with increasing collisionality in the simulations. Two types of Langevin-operator, ion-ion collision models were implemented in the simulations. In both models used the collisions are functions of the local ion temperature and density, but the collisions have no velocity dependence in the first model. In the second model, the collisions are also functions of the energy of the ion that is being scattered so as to represent a Fokker-Planck collision operator. Collisions decorrelate the ions from the acoustic waves in SBS, which disrupts ion trapping in the acoustic wave. Nevertheless, ion trapping leading to a hot ion tail and two-dimensional physics that allows the SBS ion waves to nonlinearly scatter remain robust saturation mechanisms for SBBS in a high-gain limit over a range of ion collisionality. SBS 2 backscatter in the presence of a spatially nonuniform plasma flow is also investigated.Simulations show that depending on the sign of the spatial gradient of the flow relative to the backscatter, ion trapping effects that produce a nonlinear frequency shift can enhance (auto-resonance) or decrease (anti-auto-resonance) reflectivities in agreement with theoretical arguments. PACS: 52.38.-r 52.65.Rr 3

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“…One critical parameter in Brillouin scattering is the ion acoustic wave intensity,n iaw /n e , wheren iaw is the perturbed electron density due to the presence of the wave andn e is the equilibrium average electron density. At high values ofn iaw /n e (> 0.1), the ion acoustic wave decays through a few different saturation mechanism, including frequency detuning [5], partial wave breaking due to bouncing motion of the trapped particles [6] and nonlinear cascades of ion acoustic waves into other types of waves [7]. Here, we show that a strong ion acoustic wave modifies the plasmon dispersion relation and generates a plasmon band gap.…”

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confidence: 94%