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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1650-1658 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of a 1018 W/cm2, 30 fs laser pulse with solid Al was simulated with the electron kinetic code "FPI" [J. P. Matte et al., Phys. Rev. Lett. 72, 1208 (1994)] in which an improved average ion module was fully coupled to the electron kinetics. It includes electron impact ionization and excitation and their inverse processes: collisional recombination and de-excitation; as well as radiative decay and pressure ionization. We compare to runs without the inverse processes, and also without atomic physics (with 〈Z〉 set to 11). Atomic physics strongly affects the energy balance and the shape of the distribution function. Line radiation is mostly due to three body recombination into excited states after the peak of the pulse, as the plasma cools down. Despite the atomic processes and the high density, strongly non-Maxwellian distribution functions were obtained due to very steep temperature gradients and strong collisional heating, at the peak of the pulse. However, after the pulse, there is a very rapid thermalization of the electron distribution to which inverse processes strongly contribute. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3518-3519 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Following earlier analyses for the planar and spherical cases, nonlocal electron radial transport is treated for cylindrical high-Z plasmas. Comparison of the result with earlier ones shows that, for the same parameters, the magnitude of the nonlocal heat flux for the cylindrical case is intermediate between the planar and spherical cases, and somewhat closer to the spherical case. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1280-1283 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of spherical geometry on nonlocal radial electron heat transport has been studied using perturbation analysis . The nonlocal expression for the radial heat flux is obtained in the limit of large ion charge. The deviation of the spherical nonlocal heat transport from the planar theory has been investigated and it has been found that the space curvature can significantly modify the heat flux compared to the planar result when the delocalization length (that associated with the faster electrons which dominate energy transport) is comparable to the radius. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3570-3576 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements are presented of electron heat transport with non-Maxwellian (flattopped) distributions due to inverse bremsstrahlung absorption of intense microwaves in the University of California at Davis Aurora II device [Rogers et al., Phys. Fluids B 1, 741 (1989)]. The plasma is created by pulsed discharge in a cylindrical vacuum chamber with surface magnets arranged to create a density gradient. The ionization fraction (∼1%) is high enough that charged particle collisions are strongly dominant in the afterglow plasma. A short microwave pulse (∼2 μs) heats a region of the afterglow plasma (ne/ncr≤0.5) creating a steep axial (LT∼1–10λei) temperature gradient. Langmuir probes are used to measure the relaxation of the heat front after the microwave pulse. Time and space resolved measurements show that the isotropic component of the electron velocity distribution is flat topped (∼exp[−(v/vm)m], m(approximately-greater-than)2) in agreement with Fokker–Planck calculations using the measured density profile. Classical heat transport theory is not valid both because the isotropic component of the electron velocity distribution is flattopped and the temperature gradients are very steep.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1412-1420 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron heat flow was computed in the context of a steadily propagating shock wave. Two problems were studied: a Mach 8 shock in hydrogen, simulated with an ion kinetic code, and a Mach 5 shock in lithium, simulated with an Eulerian hydrodynamic code. The electron heat flow was calculated with Spitzer–Härm classical conductivity, with and without a flux limit, and several nonlocal electron heat flow formulas published in the literature. To evaluate these, the shock's density, velocity, and ion temperature profiles were fixed, and the electron temperature and heat flow were compared to those computed by an electron kinetic code. There were quantitative differences between the electron temperature profiles calculated with the various formulas. For the Mach 8 shock in hydrogen, the best agreement with the kinetic simulation was obtained with the Epperlein–Short delocalization formula [Phys. Fluids B 4, 2211 and 4190 (1992)], and the Luciani–Mora–Bendib formula [Phys. Rev. Lett. 55, 2421 (1985)] gave good agreement. For the Mach 5 shock in lithium, both of these gave good agreement. The earlier Luciani–Mora–Virmont formula [Phys. Rev. Lett. 51, 1664 (1983)] gave fair agreement, while that of San Martin et al. [Phys. Fluids B 4, 3579 (1992); 5, 1485 (1993)] was even further off than the classical Spitzer–Härm [Phys. Rev. 89, 977 (1953)] formula for thermal conduction. To assess the effect of nonlocal electron heat flow on the shock's hydrodynamics and ion kinetics, each of the two problems was done with two different electron heat flow models: the classical Spitzer–Härm local heat conductivity, and the Epperlein–Short nonlocal electron heat-flow formula. In spite of the somewhat different electron temperature profiles, the effect on the shock dynamics was not important. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis is presented of K-shell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 μm) at 1018–1019 W/cm2. Stark broadening measurements of He-like and Li-like lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce x-ray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest x-ray pulse at a given wavelength is relatively narrow. Lower intensity produces a short x-ray pulse but low brightness. The x-ray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximately 6% of the laser energy is coupled to the target at 1018 W/cm2 (1% in thermal electrons with Te≈0.6 keV and 5% in suprathermal electrons with Th≈25 keV). At Iλ2=1018 W μm2/cm2 (no prepulse) around 1010 photons are emitted per laser shot, in 2π srd in cold Kα radiation (2–9 A(ring), depending on the target material) and up to 2×1011 photons are obtained in 2π srd with the unresolved transition array (UTA) emission from the Ta target. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3182-3190 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion kinetic simulations of the formation and propagation of planar shock waves in a hydrogen plasma have been performed at Mach numbers 2 and 5, and compared to fluid simulations. At Mach 5, the shock transition is far wider than expected on the basis of comparative fluid calculations. This enlargement is due to hot ions streaming from the hot plasma into the cold plasma and is found to be limited by the electron preheating layer, essentially because electron–ion collisions slow down these energetic ions very effectively in the cold upstream region. Double-humped ion velocity distributions formed in the transition region, which are particularly prominent during the shock formation, are found not to be unstable to any electrostatic mode, due to electron Landau damping. At Mach numbers of 2 and below, no such features are seen in velocity space, and there is very little difference between the profiles from the kinetic and fluid simulations.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 485-491 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron kinetics is considered in a plasma in which the distribution of ion charge stages is far from the coronal equilibrium. In rapidly ionizing plasmas, radiative cooling and ionization are found to cause the electron distribution to deviate significantly from a Maxwellian. The relevance of such distribution functions to divertor plasmas near the neutralizer plate is discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 167-175 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption and x-ray emission results obtained with a 1 psec pulse incident on solid targets with an intensity between 1011 and 1016 W/cm2 are presented and discussed. For I〈5×1014 W/cm2, submicron density gradient scale lengths (L/λ≤0.2) are measured and the comparison of calculated and experimental values of absorption for aluminum indicates a relatively good agreement for p polarization and noticeable differences for s polarization. X-ray conversion efficiencies have been obtained in the sub-keV and keV range. At high intensities (I〉1015 W/cm2) an evaluation of the plasma parameters is obtained from high resolution keV spectra. Finally, the results are discussed in the light of 1-D hydrodynamic simulations with time-dependent atomic physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 741-749 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Temporal and spatial measurements of electron heat transport are made in the University of California Davis AURORA device (J. H. Rogers, Ph.D. dissertation, University of California, Davis, 1987). In AURORA, a microwave pulse heats a region of underdense, collisional, plasma (n/ncr (approximately-less-than)1, where ncr =1.8×1010 cm−3 is the critical density, Te0 ≈0.15 eV, and the electron scattering mean free path λ⊥(approximately-greater-than)2 cm). In this region, strong thermal heating (Tc (approximately-less-than)0.7 eV) as well as suprathermal heating (Th≈3 eV) is observed. The strong heating results in a steep temperature gradient that violates the approximations of classical heat diffusion theory (LT/λ⊥(approximately-greater-than)3 for thermal electrons, where LT=Tc(∂Tc/∂z)−1 is the cold electron temperature scale length. The time evolution of the electron temperature profile is measured using Langmuir probes. The measured relaxation of the temperature gradient after the microwave pulse is compared to calculations using the Fokker–Planck International code [Phys. Rev. Lett. 49, 1936 (1982)] and the multigroup, flux-limited, target design code lasnex [Comm. Plasma Phys. 2, 51 (1975)]. The electron distribution function at the end of the microwave pulse is used as initial conditions for both codes. The Fokker–Planck calculations are found to agree very well with the measurements. However, the flux-limited diffusion calculations do not agree with the measurements for any value of the flux limiter.
    Type of Medium: Electronic Resource
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