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  • 1
    Electronic Resource
    Electronic Resource
    Thomson scattering from laser plasmas : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2117-2128 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering has recently been introduced as a fundamental diagnostic of plasma conditions and basic physical processes in dense, inertial confinement fusion plasmas. Experiments at the Nova laser facility [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)] have demonstrated accurate temporally and spatially resolved characterization of densities, electron temperatures, and average ionization levels by simultaneously observing Thomson scattered light from ion acoustic and electron plasma (Langmuir) fluctuations. In addition, observations of fast and slow ion acoustic waves in two-ion species plasmas have also allowed an independent measurement of the ion temperature. These results have motivated the application of Thomson scattering in closed-geometry inertial confinement fusion hohlraums to benchmark integrated radiation-hydrodynamic modeling of fusion plasmas. For this purpose a high energy 4ω probe laser was implemented recently allowing ultraviolet Thomson scattering at various locations in high-density gas-filled hohlraum plasmas. In particular, the observation of steep electron temperature gradients indicates that electron thermal transport is inhibited in these gas-filled hohlraums. Hydrodynamic calculations which include an exact treatment of large-scale magnetic fields are in agreement with these findings. Moreover, the Thomson scattering data clearly indicate axial stagnation in these hohlraums by showing a fast rise of the ion temperature. Its timing is in good agreement with calculations indicating that the stagnating plasma will not deteriorate the implosion of the fusion capsules in ignition experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873499
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  • 2
    Electronic Resource
    Electronic Resource
    Growth of the Rayleigh–Taylor instability in an imploding Z-pinch (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 737-747 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rayleigh–Taylor (RT) instability of cylindrical, imploding plasma liners in a Z-pinch is analyzed. The reduction in total perturbation growth for multicascade systems (multiple imploding shells) is presented. This reduction is effective if the pressure produced by the impacting shell exceeds the magnetic pressure at the time of impact. Analytical and numerical solutions are also obtained for the RT instability of an imploding plasma liner accelerated into undisturbed plasma. The snowplow model is used in which the mass encountered by the imploding magnetic piston is swept into an infinitely thin sheath. A shock front launched ahead of the liner is shown to reduce the growth rate. It is also shown that accumulating the mass increases the growth rate. However, the total perturbation growth can be reduced if the liner accumulates the mass during the implosion compared to a liner with the same mass imploding into vacuum. Finally, it is shown that the final kinetic energy density for a given shell nonuniformity is largest if the final liner mass is accumulated during the implosion. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872168
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetohydrodynamic solution for a Z pinch showing the production of a hot spot (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1737-1740 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional LASNEX [National Technical Information Service Document No. DE 81026329 (Zimmerman, Report No. UCRL-74811, 1973)] calculations are made for a Z pinch on Saturn, the low-impedance, low-inductance electron accelerator at the Sandia National Laboratories [D. D. Bloomquist et al. Proceedings of the Sixth IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (Institute of Electronics and Electrical Engineers, New York, 1987), p. 310]. The experiment is characterized by a current of 6 MA with a tungsten wire load (4 mg) at 2 mm. Two-dimensional calculations show the evolution of the Rayleigh–Taylor instability to the bubble and spike phase, causing high-density islands to form in the pinch opposite the bubbles. The two-dimensional energy flow causes a "hot spot'' to evolve, which is shown to agree in its size and brightness with pinhole camera measurements. This is the first explicit calculation of a hot spot in two dimensions employing the full magnetohydrodynamic equations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871691
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  • 4
    Electronic Resource
    Electronic Resource
    Electron heat transport with non-Maxwellian distributions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3570-3576 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.870892
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  • 5
    Electronic Resource
    Electronic Resource
    Low allergenicity of clonidine impedes studies of sensitization mechanisms in guinea pig models (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Contact dermatitis 23 (1990), S. 0 
    Details
    ISSN: 1600-0536
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: During clinical mills, a clonidine transdermal device has been found to induce clonidine-specific allergic contact dermatitis in up to 25% of patients during a treatment period of 1 year. Using 3 different guinea pig strains, development was attempted of an experimental guinea pig model that would allow for in-depth studies into the mechanism of sensitization, and a possible role of transdermal device components. Transient low-level clonidine allergy could be obtained only in a minority of animals, with severe sensitization procedures departing from epicutaneous applications, combined with intradermal (adjuvant) FCA injections. Sensitization was not potentiated by additional booster procedures, including cyclophosphamide pretreatment, nor any of the putative cofactors (UV-treatments, C. parvum or acetaldehyde involvement) studied. These results suggest that the persistent skin contacts in man with transdermal devices for sustained drug delivery, generate unique conditions favouring the development of allergic contact dermatitis, which are difficult to mimic in experimental animal models. Thus, clinical allergy may develop even lo extremely weak sensitizing drugs that can be safety used orally, and escape most currently available predictive contact allergy animal models Clinical studies remain unavoidable for studying factors that may reduce sensitization rates to more acceptable levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0536.1990.tb03228.x
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  • 6
    Electronic Resource
    Electronic Resource
    Anomalous thermal electron heating and heat transport inhibition due to parametric instabilities (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1150-1153 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements are presented of strong thermal electron heating and the heat transport inhibition. An electron plasma wave heats hot electrons near the critical density. A return current is induced to keep charge neutrality. Thermal electrons are heated strongly by the resistivity of parametrically excited isotropic ion wave turbulence (anomalous joule heating). The heat transport of thermal electrons is also inhibited by the resistivity. The experimental results agree reasonably well with theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859250
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  • 7
    Electronic Resource
    Electronic Resource
    Eigenvalue solution for the ion-collisional effects on ion-acoustic and entropy waves (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1430-1439 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linearized ion Fokker–Planck equation is solved as an eigenvalue problem under the condition of collisionless electrons in the quasineutral limit (φ=0) for ionization-temperature ratios, ZTe/Ti=2, 4, and 8 for entropy waves and ionization-temperature ratios, ZTe/Ti=4, 8, 16, 32, 48, 64, and 80 for ion-acoustic waves. The perturbed ion distribution function for the ion-acoustic and entropy waves is formed from a Legendre polynomial expansion of eigenvectors and can be used to calculate collisionally dependent macroscopic quantities in the plasma such as gamma (Γ=Cp/Cv), the ratio of specific heats, and the ion thermal conductivity (κi).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860883
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  • 8
    Electronic Resource
    Electronic Resource
    Detailed 266 nm Thomson scattering measurements of a laser-heated plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1576-1584 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Collective Thomson scattering at 266 nm is used to obtain spatially resolved, two-dimensional electron density, temperature, and radial drift profiles of a collisional laser plasma (critical density, nc =1×1021 cm−3). An ultraviolet diagnostic wavelength minimizes the complicating effects of inverse bremsstrahlung and refractive turning in the coronal region of interest, where electron densities approach nc/10. Laser plasmas of this type are important because they model some of the aspects of the plasmas found in high-gain laser-fusion pellets irradiated by long pulse widths (tL(approximately-greater-than)10 nsec), where laser light is absorbed mostly in the corona. The experimental results and lasnex [Comments Plasma Phys. Controlled Fusion 2, 51 (1975)] simulations agree within a percent standard deviation of 40% for electron density and 50% for electron temperature and radial drift velocity. Thus it is shown that the hydrodynamics equations with classical coefficients and the numerical approximations in lasnex are valid models of laser-heated, highly collisional plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860066
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  • 9
    Electronic Resource
    Electronic Resource
    Density and temperature profiles in strongly absorbing plasma with distributed absorption (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1241-1244 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model is presented of the spatial structure of a laser-heated, strongly absorbing, planar plasma. Inverse bremsstrahlung is very strong so that laser light absorption is not localized. Absorption is distributed over densities from well below critical to the critical density. It is shown that the spatial structure of the plasma is self-consistent with laser energy deposition and heat transport so measurement of the plasma structure can be used as diagnostic of absorption and transport. Nonphysical discontinuities in density and temperature at the critical surface that are predicted by previous local absorption models for strongly flux-limited heat transport are reduced. These jumps persist in the present model. It is shown that an improved flux-limited heat transport model, strongly limited in the underdense plasma and weakly limited in the overdense plasma, results in continuous density and temperature profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859817
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  • 10
    Electronic Resource
    Electronic Resource
    Particle simulations of plasma and dielectric Cerenkov masers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 908-915 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new particle simulation model has been developed to investigate Cerenkov masers. The novel aspects of the code are briefly described, and results of simulations of two types of Cerenkov masers are presented. The first device uses a conventional dielectric lining as its slow-wave structure. The second is a new type of Cerenkov maser in which a circular waveguide is partially filled with a dense annular plasma instead of a dielectric layer. Both simulations agree well with experimental results and linear theory calculations. Saturation of the instability is shown to be due to trapping of the beam electrons. The relative merits of each system are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866774
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