Thomson Scattering Measurements of Saturated Ion Waves in Laser Fusion Plasmas

Glenzer, S. H.; Divol, L.; Berger, R. L.; Geddes, C. G. R.; Kirkwood, R. K.; Moody, J. D.; Williams, E. A.; Young, P. E.

doi:10.1103/physrevlett.86.2565

Cited by 64 publications

(41 citation statements)

References 26 publications

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“…These simulations results and those reported in Refs. 1 and 2 support recent experimental observations of the importance of ion trapping effects 19,20 and the two-ion-wave decay 21,22 associated with SBS.…”

Section: Introductionsupporting

confidence: 74%

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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Section: Introductionsupporting

confidence: 74%

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

et al. 2006

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“…Stimulated Raman backscatter was even smaller (< 1%). This small SBS was somewhat unexpected given the large SBS ( > ∼ 30%) reported from gasbags filled with CO 2 to equivalent fully ionized electron densities [4] and the fact that ion acoustic waves in CO 2 and Krypton plasmas have similar dispersion properties. The ion Landau damping is negligible and the electron Landau damping ν a is small, about 0.01ω a where ω a ∼ k ZT e /m i .…”

Section: Introductionmentioning

confidence: 90%

“…Previous experiments [3,4] and subsequent modeling [7] have also shown the need for nonlinear processes that limit the ion acoustic wave amplitude. Here, we show that the same nonlinear modeling applies successfully to both CO 2 with 25-30% SBS and Krypton plasmas with 1-5% SBS provided the laser propagation through the entire plasma, including the blast waves, is included.…”

Section: Introductionmentioning

confidence: 99%

“…Experiments with hohlraum targets at the former NOVA Laser Facility [2] measured SBS that was consistent with scattering from gold plasma that was ablated from the hohlraum wall. [3] In order to better understand the nonlinear SBS interaction for weakly damped ion acoustic waves, CO 2 gasbag plasmas were used in experiments at NOVA [4] as a surrogate for gold in studying SBS in long scale length plasma because of the difficulties of creating long scale length gold plasmas. However, collisional processes are much stronger in gold than CO 2 .…”

Section: Introductionmentioning

confidence: 99%

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Laser light backscatter from intermediate and high Z plasmas

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In experiments at the Omega Laser Facility, stimulated Brillouin backscatter (SBS) from gasbags filled with Krypton and Xenon gases was unexpectedly 10 times lower than from CO 2 -filled gasbags with similar electron densities. The SBS backscatter was a 1-5 % for both 527nm and 351nm interaction beams at an intensity of ∼ 10 15 W/cm 2 . The SRS backscatter was less than 1%. The 351nm interaction beam is below the threshold for filamentation and all the SBS occurs in the density plateau between the blast waves. Inverse bremsstrahlung absorption of the incident and SBS light account for the lower reflectivity from Kr than from CO 2 . The 527nm interaction beam filaments in the blowoff plasma before the beam propagates through the blast wave where it is strongly absorbed. Thus, most of the 527nm SBS occurs in the flowing plasma outside the blast waves. Nonlinear processes that limit the acoustic wave amplitudes to 1% of electron density model the SBS reflectivity well in both CO 2 and Krypton plasmas . * Electronic address: berger5@llnl.gov

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“…The Brillouin scattering plays an important role in inertial confinement fusion [1][2][3] and pulse compression [4]. 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.…”

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confidence: 99%