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  • 1
    Electronic Resource
    Electronic Resource
    Saturation of stimulated Brillouin scatter by self-consistent flow profile modification in laser hot spots (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 437-446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scattering instabilities, such as stimulated Brillouin scatter (SBS) and stimulated Raman scatter (SRS), transfer momentum to the plasma which leads to flow inhomogeneities in laser hot spots that may significantly reduce the level of SBS. Simple estimates and simulations shown that the magnitude of flow fluctuations can reach Mach numbers of order unity in a time scale of hundreds of picoseconds. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872102
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  • 2
    Electronic Resource
    Electronic Resource
    Laser beam deflection by flow and nonlinear self-focusing (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1709-1727 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In general, it is found that the plasma density response to a laser beam's ponderomotive force is shifted in the direction of a transverse flow, which in turn deflects the laser beam in that direction, and retards the flow at a temporal rate which is proportional to the beam's spatial deflection rate. This rate is a rapidly increasing function of 〈I〉, the average laser intensity. This may result in finite beam deflections after propagation over a distance of a few speckle lengths for random phase plate optics. In current gas filled hohlraum experiments, the estimated magnitude of these effects is consistent with their experimental observation and one may need to include this physics in order to predict beam pointing which results in a symmetric capsule implosion. Flow retardation may be sufficient to exclude flow from the beam, self-limiting the deflection process. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871690
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  • 3
    Electronic Resource
    Electronic Resource
    A self-consistent trapping model of driven electron plasma waves and limits on stimulated Raman scatter (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4784-4799 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Vlasov equation based model is used to determine various regimes of electron plasma wave response to a source appropriate to stimulated scatter in a laser hot spot. It incorporates trapped particle effects such as the standard nonlinear frequency shift, extended beyond the weak regime, and a reduction of damping à la Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, JETP 16, 351 (1963)]. The results are consistent with those of Holloway and Dorning [J. P. Holloway and J. J. Dorning, Phys. Rev. A 44, 3856 (1991)] for small amplitude Bernstein–Greene–Kruskal modes. This leads to the prediction that as long as kλD≥0.53 for a background Maxwellian distribution function, e.g., a 5 keV plasma with ne/nc≤0.075, anomalously large backward stimulated Raman scatter can be excluded. A similar analysis leads to density limits on stimulated Brillouin scatter. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410111
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  • 4
    Electronic Resource
    Electronic Resource
    Nonlinear theory of power transfer between multiple crossed laser beams in a flowing plasma (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1461-1466 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytic results are obtained for power transfer among crossing, equal frequency, laser beams, each smoothed by a random phase plate, in a flowing homogeneous plasma. For beams with well-separated directions, interbeam coupling transfers power, while intrabeam coupling causes beam deflection. For any pair of such beams, the beam with the largest positive projection on the flow direction will drain power from the other. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872804
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  • 5
    Electronic Resource
    Electronic Resource
    Model simulations of Langmuir wave turbulence induced by the Raman instability (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3876-3885 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One and two dimensional simulations of a variant of Zakhavov's equations of nonlinear Langmuir wave dynamics, driven by a model source owing to Stimulated Raman backscatter (SRS) at wavenumber k1, yield constitutive relations between the energy injection rate, 〈ε〉, from SRS, and various local Langmuir wave turbulence properties, such as the mean spatial and spectral energy densities and effective damping rate, νeff. In the inertial regime, where the Langmuir wave damping is significant only for k〉k1, it is found that these relations are insensitive to the source bandwidth, ν, if ν≥νeff, and are well represented by power laws in 〈ε〉. Approximate scaling relations of νeff with the ion acoustic damping rate coefficient, νia, show that the turbulence is over-stable with respect to the Langmuir decay instability, as determined by νia and νeff, by a factor of order unity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873107
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  • 6
    Electronic Resource
    Electronic Resource
    Measurements of laser-plasma instability relevant to ignition hohlraums : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1849-1856 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The potential for laser-plasma instability is a serious concern for indirect-drive inertial confinement fusion (ICF), where laser beams illuminate the interior of a cavity (called a hohlraum) to produce x-rays for imploding a fusion capsule symmetrically. The speckled nature of laser beams used in ICF is an important factor in laser-plasma instability processes. For example, models which calculate the spatial growth of convective instability by properly accounting for the laser speckles successfully predict the observed onsets of backscattering due to stimulated Brillouin and Raman scattering instabilities (SBS and SRS). Assuming pump depletion as the only saturation mechanism in these models results in very large predicted levels of SBS and SRS backscattering from the long-scale plasmas expected in ignition hohlraums. However, in the long-scale plasmas studied in the Nova and Trident lasers [E. M. Campbell, Rev. Sci. Instrum. 57, 2101 (1986) and N. K. Moncur et al., Appl. Opt. 34, 4274 (1995)], SRS and SBS are observed to saturate much below the levels expected from pump depletion. While the mechanism of SBS saturation is not understood at present, the observations of SRS saturation are qualitatively understood. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872328
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  • 7
    Electronic Resource
    Electronic Resource
    Dependence of stimulated Brillouin scattering on focusing optic F number in long scale-length plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1091-1095 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The onset of stimulated Brillouin scattering (SBS) has been examined by varying the effective F number (lens focal length/incident beam diameter) of the optical system used to irradiate a performed 1 mm long, longitudinally uniform hydrocarbon (CH) plasma. SBS onset occurs at higher average laser intensity for smaller F, in qualitative agreement with theory. Quantitative comparison between theory and experiment, and implications for the National Ignition Facility [Phys. Plasmas 2, 2480 (1995)] are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871764
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  • 8
    Electronic Resource
    Electronic Resource
    Reduced description of strong Langmuir turbulence from kinetic theory (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 76-96 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A reduced description of strong Langmuir turbulence is derived from the Vlasov–Poisson equations by using an oscillation center transformation that decomposes the distribution function into envelope components which vary slowly on the plasma frequency time scale. The familiar high-frequency response is identified in the context of a basic ordering of small quantities. A generalization of the ion acoustic wave equation to the regime of equal electron and ion temperatures which is valid in this ordering is derived using a three-pole approximant for the collisionless ion susceptibility. The resulting extended Zakharov model is solved numerically in two dimensions for parameters relevant to radio-frequency heating of the ionosphere, producing energy and power spectra of fluctuations that are qualitatively similar to experimental observations. A new local quasilinear equation for the spatial and temporal evolution of the slowly varying part of the oscillation center distribution function is proposed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871119
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  • 9
    Electronic Resource
    Electronic Resource
    A test-bed for Langmuir wave turbulence modeling of stimulated Raman backscatter (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 476-484 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated Raman backscatter (SRS) may incorporate several, qualitatively different regimes of Langmuir wave dynamics, as it grows convectively in space. These typically include a strictly linear regime at the far end of the plasma from the laser, where SRS comes up from thermal Langmuir wave fluctuations; which may progress to a regime where the primary SRS daughter Langmuir wave is unstable to the Langmuir wave decay instability (LDI); and perhaps to a regime of strong Langmuir wave turbulence (SLT). The accurate description of the spatial transition between these regimes, which may involve large Langmuir wave correlation lengths, is a great challenge for turbulence modeling. In this paper a highly idealized model of SRS in periodic geometry is introduced which allows for the presence of a unique Langmuir wave regime for a given set of physical parameters, and therefore presents the minimal challenge for a turbulence model. One- and two-dimensional simulations of this SRS model, which allows for LDI and SLT as described by Zakharov's model of nonlinear Langmuir wave dynamics, are compared with the predictions of a recently introduced turbulence model, and quantitative agreement is obtained, without the use of any ad hoc parameters, for the SRS reflectivity and correlation length, and Langmuir and acoustic wave energy densities, over an order of magnitude variation of SRS growth rate and ion acoustic damping rate. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873214
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of smoothing by spectral dispersion on flow induced laser beam deflection: The random phase modulation scheme (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 775-781 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical results are presented for the effect of random phase modulated smoothing by spectral dispersion on flow induced laser beam deflection. It is shown that in the limit of a large number of color cycles, Ncc, the effect is identical to that of the induced spatial incoherence method of temporal smoothing. For small Ncc, the beam deflection rate may be significantly larger in the direction perpendicular to the dispersion, than in the parallel direction. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872763
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