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  • 1
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    Different kλD regimes for nonlinear effects on Langmuir waves (2006)
    American Institute of Physics
    Details
    Publication Date: 2006-05-01
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics
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  • 2
    Electronic Resource
    Electronic Resource
    High-power high-frequency-induced Langmuir turbulence in the smooth ionosphere at Arecibo. I. Theoretical predictions for altitude-resolved plasma line radar spectra (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 791-801 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This is the first of two papers comprising a theoretical and observational study of new, altitude-resolved, observations at Arecibo of Langmuir turbulence induced in the ionosphere by a powerful high-frequency (hf) heater operated at very low duty cycles. As shown in paper II [Cheung et al., Phys. Plasmas 8, 802 (2001)], higher power enabled the first observation at Arecibo of the well-developed decay-cascade features in the Thomson scatter radar power spectrum at the unmodified matching altitudes. New theoretical predictions are presented here for the parameters of these observations emphasizing the altitude and pump power dependence of the radar spectra and the time dependence of the spectra from the decaying spectra following heater switch-off. Further details of the strong turbulence signatures from higher altitudes are also presented. At the lower matching altitudes the increase, with hf power, of the angular width of the well-developed decay-cascade spectrum allows these spectral features to come into the view of the Arecibo radar. The favorable comparison of the simulation predictions and observations is discussed in the second paper. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345703
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  • 3
    Electronic Resource
    Electronic Resource
    Quantitative comparison of reduced-description particle-in-cell and quasilinear-Zakharov models for parametrically excited Langmuir turbulence (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2824-2841 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of kinetic processes on the saturation of parametric instabilities in an electromagnetically driven plasma is investigated. A reduced-description particle-in-cell technique is used as a benchmark to test a new quasilinear-Zakharov model which accounts for electron heating due to Landau damping by coupling the quasilinear diffusion equation to the Zakharov equations. The reduced-description particle-in-cell method utilizes a two-time-scale approximation which significantly reduces the numerical dissipation and ion noise levels. This approach allows accurate modeling of Langmuir and ion acoustic waves in regimes typically studied with Zakharov simulations. The comparison of the two models is performed for the test case of a one-dimensional homogeneous plasma driven by a spatially uniform pump in both the Langmuir decay instability cascade and collapse regimes. Good agreement is found in both weakly and strongly driven regimes for the total Langmuir wave energy and evolved electron velocity distributions. Electron heating significantly decreases saturation levels in strongly driven regimes by increasing the Landau damping rate, bringing the quasilinear-Zakharov simulations in much closer agreement with the reduced-description particle-in-cell simulations than standard Zakharov simulations, which do not account for the evolution of the electron distribution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874132
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of kinetic processes on Langmuir turbulence : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1723-1731 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Kinetic processes are shown to be crucial in determining the saturation level of stimulated Raman scattering for regimes relevant to NOVA [Campbell et al., Fusion Technol. 21, 1344 (1992)] and the National Ignition Facility [Lindl, Phys. Plasmas 2, 3933 (1995)]. To investigate these kinetic effects, the Zakharov, quasilinear-Zakharov, and reduced-description particle-in-cell simulation models are compared in the test case of a uniformly driven plasma. Good agreement is observed between all three simulation methods for relatively low primary Langmuir wave numbers (k1λDe∼0.1) in weakly driven regimes. In the strongly driven case, quasilinear diffusion provides an important correction to the Landau damping rate, producing saturation levels in agreement with reduced-description particle-in-cell simulations, in contrast to pure Zakharov simulations, which overestimate the saturation significantly. At higher k1λDe∼0.25, both the quasilinear-Zakharov and pure Zakharov models fail. In this regime, the autocorrelation time of the Langmuir wave spectrum is much larger than the quasilinear diffusion time, causing the quasilinear diffusion approximation to break down. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873991
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  • 5
    Electronic Resource
    Electronic Resource
    Collisional regimes of radiation-driven Langmuir turbulence (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1947-1960 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical solutions of the Zakharov equations for a plasma driven above the electron plasma frequency by a long-wavelength radiation pump can be applied to both ionospheric modification experiments and laboratory laser-plasma interactions. A key difference between these two environments is the much larger collisional damping of Langmuir waves near the critical density in laser plasmas. Zakharov equation simulations in one and two dimensions reveal a significant change in the character of the saturated turbulence state of the electromagnetic ion-acoustic decay instability for pump strengths near threshold as the collisional damping is increased to values appropriate to certain (low-intensity) laboratory laser-plasma experiments [Phys. Fluids B 3, 1983 (1991)]. The linear-instability is then characterized by the coupling of the up- and downshifted Langmuir decay modes. A new turbulence regime differing from existing models of both weak and strong turbulence is found, which is characterized by a sequence of narrow peaks in the Langmuir frequency spectrum and a nonlinearly broadened wave-vector spectrum centered near the linearly most unstable modes. Results in this regime may be relevant to second harmonic emission experiments [Phys. Fluids B 3, 1983 (1991)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871455
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  • 6
    Electronic Resource
    Electronic Resource
    Laser–plasma interactions in ignition-scale hohlraum plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2029-2040 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scattering of laser light by stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is a concern for indirect drive inertial confinement fusion (ICF). The hohlraum designs for the National Ignition Facility (NIF) raise particular concerns due to the large scale and homogeneity of the plasmas within them. Experiments at Nova have studied laser–plasma interactions within large scale length plasmas that mimic many of the characteristics of the NIF hohlraum plasmas. Filamentation and scattering of laser light by SBS and SRS have been investigated as a function of beam smoothing and plasma conditions. Narrowly collimated SRS backscatter has been observed from low density, low-Z, plasmas, which are representative of the plasma filling most of the NIF hohlraum. SBS backscatter is found to occur in the high-Z plasma of gold ablated from the wall. Both SBS and SRS are observed to be at acceptable levels in experiments using smoothing by spectral dispersion (SSD). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872000
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Evolution to turbulence in a capacitor model of resonance absorption (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1907-1916 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of a powerful, subpicosecond laser pulse with plasma is modeled within the capacitor model by means of one-dimensional electrostatic particle code. The temporal profile of the laser pulse and the growth of the electron energy by several orders of magnitude were taken into account providing adequate temporal and spatial resolution. It is shown that initially, a coherent structure is excited, and growth of plasma waves results in wave breaking and acceleration of electrons followed with decreasing intervals between them, accelerating electrons in both directions. Finally the system evolves to a state of moderate Langmuir turbulence where E2/(16πnT)(very-much-less-than)1 due to the strong heating of plasma electrons and the decrease of excited plasma wave fields. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871278
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  • 10
    Electronic Resource
    Electronic Resource
    Vlasov simulation of modulational instability and Langmuir collapse (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1129-1139 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vlasov simulations are developed to study the one-dimensional modulational instability and Langmuir collapse in a plasma driven by an external field. Both electrons and ions in the plasma are described by the Vlasov equations. The external driving field energy density is ∼10−3 times the initial electron thermal energy density. The plasma has a mass ratio of mi/me=1836, and a temperature ratio of Ti/Te=0.1 or 1.0, where mi, me, Ti, and Te are the ion mass, electron mass, ion temperature, and electron temperature. The modulational instability is saturated by the formation of Langmuir cavitons which later collapse and burn out due to the strong wave–particle interactions. The particle heating during a single Langmuir collapse is small under this weak driving field. The accelerated electron and ion jet-like streams in phase space as well as the nucleation of cavitons are observed during the evolution. Zakharov equations with the same parameters and similar initial conditions are also simulated, and the results are compared with those of the Vlasov simulations. The two models agree with each other quantitatively up to the first collapse following the saturation of exponential growth; dynamic differences appear after the first collapse. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871391
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