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  • 1
    Electronic Resource
    Electronic Resource
    Target compression by working fluids driven with solid liner implosions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 637-647 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Compression by a spherical solid liner of a gold target surrounded by a hydrogen plasma is simulated. Two-dimensional simulations that treat only a subset of the physics included in the one-dimensional code were performed in an attempt to assess multidimensional effects. A one-dimensional numerical code has been developed to study the effects of thermal radiation and conduction. Results of pressure, density, and energy deposited for different initial plasma conditions are presented and discussed. Results from both one- and two-dimensional codes show that the average target density at peak compression is 39–43 g/cm3, using the SHIVA Star facility at 90 kV discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357805
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  • 2
    Electronic Resource
    Electronic Resource
    Formation of plasma working fluids for compression by liner implosions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3769-3776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Research on the formation of a hot hydrogen working fluid, which may be used in multiple concentric solid-density liner implosions, is reported. In such implosions, an axisymmetric outer liner is driven by a multi-megamp axial discharge, and a coaxial inner liner is driven by a working fluid contained between the liners. The fluid is shocklessly compressed to high pressure as the outer liner implodes around it. In the work reported here a 10 to 100 Torr pressure, hydrogen filled coaxial gun discharge was used to inject plasma into a diagnostic chamber simulating an interliner volume. Spectroscopically determined electron densities of between 1017 and 1018 cm−3 and electron temperatures in the 0.5–2.0 eV range were obtained with a fair degree of reproducibility and symmetry. Two-dimensional, time-dependent magnetohydrodyna- mic computer simulations of the working fluid formation experiment have been performed, and the computations suggest that the present experiment achieves electron number densities and temperatures at the lower extreme of these limits, and neutral densities ∼ 0.3–1.0 ×1019 cm−3. The simulations further suggest that the upper range, and beyond, can be achieved in a more energetic version of the present experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356051
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  • 3
    Electronic Resource
    Electronic Resource
    Plasma-implosion-driven, photoionization-pumped, soft x-ray laser targets (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4112-4122 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Designs are proposed, based on a series of one-dimensional calculations, for layered, hollow cylindrical targets to be placed on the axis of an imploding, hollow Z-pinch plasma that can create the approximate plasma conditions, as well as radiation spectrum, for a photoionization pumped, Ne-like recombination laser. The lasant must reach the Ne-like state and be at the appropriate density at the same time that the photoionizing pump radiation is present, placing severe constraints on designs for such targets. Target designs are further constrained by the fact that the 3s-2p resonance line, which depopulates the lower lasing state, must not be highly trapped and by the fact that the upper lasing state must not be collisionally depopulated. We find that hollow, cylindrical targets consisting of a few-micron-thick CH strongback, coated on the inside with a thin layer of Ni lasant and on the outside with an Al converter layer, can be optimized to achieve appropriate conditions for lasing and modest levels of gain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343996
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  • 4
    Electronic Resource
    Electronic Resource
    Optimization of soft x-ray emission from stagnating compact toroidal plasmas: A computational study (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 873-879 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computational simulations aimed at optimizing the high-energy, high-power, multikilovolt electromagnetic radiation emitted by a rapidly moving compact toroidal (CT) plasma which stagnates against a stationary "wall" are performed for argon, krypton, and xenon plasmas over a range of CT parameters. CT kinetic energies vary from 2–10 MJ, impact speeds vary from 50–200 cm/μs, and CT masses vary from 5–11 mg. It is found that a 2 MJ Ar CT optimally emits 1–1.5 MJ of essentially K-line radiation (〉3 keV) for impact speeds of about 60–90 cm/μs; a 10 MJ Kr CT optimally emits about 1 MJ of essentially K-line radiation (〉12.5 keV) for impact speed of about 135 cm/μs; and a 10 MJ Xe CT optimally emits about 3 MJ of essentially L-line radiation (〉5 keV), about 0.5 MJ of continuum radiation above 10 keV, and about 0.1 MJ of continuum radiation above 20 keV, all also for impact speed of about 135 cm/μs. Pulse widths vary for the above optima from 7 ns at 135 cm/μs to 30 ns at 60 cm/μs. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872179
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  • 5
    Electronic Resource
    Electronic Resource
    Hydromagnetic Rayleigh–Taylor instability in high-velocity gas-puff implosions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1477-1484 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments using the Saturn pulsed power generator have produced high-velocity z-pinch plasma implosions with velocities over 100 cm/μs using both annular and uniform-fill gas injection initial conditions. Both types of implosion show evidence of the hydromagnetic Rayleigh–Taylor instability with the uniform-fill plasmas producing a more spatially uniform pinch. Two-dimensional magnetohydrodynamic simulations including unsteady flow of gas from a nozzle into the diode region have been used to investigate these implosions. The instability develops from the nonuniform gas flow field that forms as the gas expands from the injection nozzle. Instability growth is limited to the narrow unstable region of the current sheath. For the annular puff the unstable region breaks through the inner edge of the annulus increasing nonlinear growth as mass ejected from the bubble regions is not replenished by accretion. This higher growth leads to bubble thinning and disruption producing greater nonuniformity at pinch for the annular puff. The uniform puff provides gas to replenish bubble mass loss until just before pinch resulting in less bubble thinning and a more uniform pinch. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872806
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  • 6
    Electronic Resource
    Electronic Resource
    A heuristic model for the nonlinear Rayleigh–Taylor instability in fast Z pinches (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2055-2062 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple, heuristic model for the early nonlinear phase of the Rayleigh–Taylor instability (RTI) in thin-cylindrical-shell Z-pinch implosions has been developed. This model is based on the fact that, as the field–plasma interface is deformed, there is a component of the applied force that acts to move mass from the low mass per unit area bubble region into the higher mass per unit area spike region. The resulting reduced mass per unit area of the bubble causes it to be preferentially accelerated ahead of the spike. The pinch begins to radiate as the bubble mass first reaches the axis, and it continues to radiate while the mass that is entrained within the spikes and within unperturbed parts of the shell also arrives on axis. This model relates the time at which the bubble arrives on axis to an initial wavelength and amplitude of a single mode of the RTI. Then, by comparing this to the time at which the unperturbed mass reaches the axis, one estimates pinch thermalization time, a quantity that is determined experimentally. Experimental data, together with analytic models, have been used to choose appropriate initial wavelength and amplitude both for foils and for certain gas puff implosions. By noting that thermalization time is a weak function of these parameters, it is argued that one may use the same values for an extrapolative study of qualitatively similar implosions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871292
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  • 7
    Electronic Resource
    Electronic Resource
    Compact toroid formation, compression, and acceleration (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2938-2958 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Research on forming, compressing, and accelerating milligram-range compact toroids using a meter diameter, two-stage, puffed gas, magnetic field embedded coaxial plasma gun is described. The compact toroids that are studied are similar to spheromaks, but they are threaded by an inner conductor. This research effort, named marauder (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation), is not a magnetic confinement fusion program like most spheromak efforts. Rather, the ultimate goal of the present program is to compress toroids to high mass density and magnetic field intensity, and to accelerate the toroids to high speed. There are a variety of applications for compressed, accelerated toroids including fast opening switches, x-radiation production, radio frequency (rf) compression, as well as charge-neutral ion beam and inertial confinement fusion studies. Experiments performed to date to form and accelerate toroids have been diagnosed with magnetic probe arrays, laser interferometry, time and space resolved optical spectroscopy, and fast photography. Parts of the experiment have been designed by, and experimental results are interpreted with, the help of two-dimensional (2-D), time-dependent magnetohydrodynamic (MHD) numerical simulations. When not driven by a second discharge, the toroids relax to a Woltjer–Taylor equilibrium state that compares favorably to the results of 2-D equilibrium calculations and to 2-D time-dependent MHD simulations. Current, voltage, and magnetic probe data from toroids that are driven by an acceleration discharge are compared to 2-D MHD and to circuit solver/slug model predictions. Results suggest that compact toroids are formed in 7–15 μsec, and can be accelerated intact with material species the same as injected gas species and entrained mass ≥1/2 the injected mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860681
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  • 8
    Electronic Resource
    Electronic Resource
    Time resolved mass flow measurements for a fast gas delivery system (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1740-1743 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique is demonstrated whereby the delivered mass and flow rate versus time of a short rise-time gas delivery system may be accurately determined. The gas mass M that flows past a point in a gas delivery system by an arbitrary time t=tp may be accurately measured if that point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values of tp, and assuming reproducibility, the injected mass time history M(t) characteristic of the system without the fast closing valve may be determined. The flow rate versus time dM(t)/dt may then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2-mm-i.d., 0.76-mm-thick copper tube is isolated by imploding (θ pinching) the tube using a single turn tungsten magnetic-field coil. Optical measurements of the tube's internal area versus time indicate that the tube is sealed in 7 μs. Results are correlated with piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the θ pinch process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144002
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  • 9
    Electronic Resource
    Electronic Resource
    Large-scale-length nonuniformities in gas puff implosions (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2677-2684 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Because they are less susceptible to the hydromagnetic Rayleigh–Taylor instability than other fast Z-pinch imploding liner systems, gas puffs offer the possibility of higher implosion velocity. This higher specific energy appears necessary for optimizing high-energy x rays required in a photoionization-pumped soft x-ray laser. Nevertheless, large-scale-length nonuniformities created as the gas flows from the nozzle across the electrode gap are a potential problem. One- and two-dimensional calculations suggest that gas near the nozzle will implode before that which is further from the nozzle, leading to an effect described as "zippering.'' Because the number of such two-dimensional calculations that can be done is limited and because the density distribution of nozzles is uncertain, we have developed a simple quasi-two-dimensional interface code that is able to quickly survey the effect of arbitrary initial gas distributions on the implosion dynamics. Results of this survey suggest that zippering contributes significantly to thermalization time, and we propose two methods to counteract this problem. These techniques, each of which involves tailoring the initial density distribution to offset effects of nonuniformities, appear promising. Nevertheless, we will never completely eliminate these nonuniformities, therefore, they must be accounted for in x-ray laser target design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336974
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  • 10
    Electronic Resource
    Electronic Resource
    Efficient x-ray production from ultrafast gas-puff Z pinches (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 830-833 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Proto-II accelerator has been used to implode krypton and xenon annular gas puffs. A significant fraction of the machine electrical energy was converted first to plasma kinetic energy and then to x rays when the plasma pinched on axis. Quantitative measurements using time-resolved bolometers have shown as much as 10% of the total radiation yield near 1 keV in Xe and 2 keV in Kr. We have compared this radiation yield to the predictions from one-dimensional magnetohydrodynamic code calculations. The implosions were also observed with both time-integrated pinhole cameras and spectrographs. No hard x-ray (E〉10 keV) output was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334734
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