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  • 1
    Electronic Resource
    Electronic Resource
    Scaling and optimization of the radiation temperature in dynamic hohlraums (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1673-1691 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quasianalytic model of the dynamic hohlraum is presented. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum radiation temperature as a function of the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and quasispherical Z pinches. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1360213
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of load thickness on the performance of high velocity, annular Z-pinch implosions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 238-248 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical calculations have been performed to investigate the role that load thickness may play in the performance of fast annular Z-pinch implosions. In particular, the effects of load thickness on the mitigation of the magnetically-driven Rayleigh–Taylor (RT) instability and energy coupling between the plasma load and generator are addressed. Using parameters representative of the Z accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories, two-dimensional magnetohydrodynamic simulations show that increased load thickness results in lower amplitude, slightly longer wavelength RT modes. In addition, there appears to be an optimum in implosion velocity which is directly associated with the thickness of the sheath and subsequent RT growth. Thin, annular loads, which should couple efficiently to the accelerator, show a large reduction in implosion velocity due to extreme RT development and increased load inductance. As a consequence, thicker loads on the order of 5 mm, couple almost as efficiently to the generator since the RT growth is reduced. This suggests that Z-pinch loads can be tailored for different applications, depending on the need for uniformity or high powers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327618
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  • 3
    Electronic Resource
    Electronic Resource
    Long implosion time tungsten wire array Z pinches on the Saturn generator (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2945-2958 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent success on the Saturn [C. Deeney et al., Phys. Rev. E 56, 5945 (1997)] and Z [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] accelerators at Sandia National Laboratories have demonstrated the ability to scale Z-pinch parameters to increasingly larger current pulsed power facilities. Next generation machines will require even larger currents (〉20 MA), placing further demands on pulsed power technology. To this end, experiments have been carried out on Saturn operating in a long pulse mode, investigating the potential of lower voltages and longer implosion times while still maintaining pinch fidelity. High wire number, 25 mm diam tungsten arrays were imploded with implosion times ranging from 130 to 240 ns. The results were comparable to those observed in the Saturn short pulse mode, with rise times on the order of 4.5–6.5 ns. Experimental data will be presented, along with two-dimensional radiation magnetohydrodynamic simulations used to explain and reproduce the experiment. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874146
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  • 4
    Electronic Resource
    Electronic Resource
    Implosion dynamics of long-pulse wire array Z pinches : 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. 1935-1944 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent improvements in Z-pinch wire array load design at Sandia National Laboratories have led to a substantial increase in pinch performance as measured by radiated powers of up to 280 TW in 4 ns and 1.8 MJ of total radiated energy. Next generation, higher-current machines will allow for larger mass arrays and comparable or higher velocity implosions to be reached, possibly extending these results. As the current is pushed above 20 MA, a conventional machine design based on a 100 ns implosion time results in higher voltages, hence higher cost and power flow risk. Another approach, which shifts the risk to the load configuration, is to increase the implosion time to minimize the voltage. This approach is being investigated in a series of experimental campaigns on the Saturn [C. Deeney et al., Phys. Plasmas 6, 3576 (1999)] and Z [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] machines. In this paper, both experimental and two-dimensional computational modeling of the first long implosion time Z experiments will be presented. The experimental data shows broader pulses, lower powers, and larger pinch diameters compared to the corresponding short pulse data. By employing a nested array configuration, the pinch diameter was reduced by 50% with a corresponding increase in power of 〉30%. Numerical simulations suggest that load velocity is the dominating mechanism behind these results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874018
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  • 5
    Electronic Resource
    Electronic Resource
    Radiative properties of high wire number tungsten arrays with implosion times up to 250 ns (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3576-3586 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High wire number, 25-mm-diameter tungsten wire arrays have been imploded on the 8-MA Saturn generator [R. B. Spielman et al., AIP Conference Proceeding 195, 3 (American Institute of Physics, Woodbury, NY 1989)], operating in a long-pulse mode. By varying the mass of the arrays from 710 to 6140 μg/cm, implosion times of 130–250 ns have been obtained with implosion velocities of 50–25 cm/μs, respectively. These Z-pinch implosions produced plasmas with millimeter diameters that radiated 600–800 kJ of x-rays, with powers of 20–49 TW; the corresponding pulsewidths were 19–7.5 ns, with risetimes ranging from 6.5 to 4.0 ns. These powers and pulsewidths are similar to those achieved with 50-ns implosion times on Saturn. Two-dimensional, radiation-magnetohydrodynamic calculations indicate that the imploding shells in these long implosion time experiments are comparable in width to those in the short-pulse cases. This can be due to lower initial perturbations. A heuristic wire array model suggests that the reduced perturbations, in the long-pulse cases, may be due to the individual wire merger occurring well before the acceleration of the shell. The experiments and modeling suggest that 150–200 ns implosion time Z-pinches could be employed for high-power, x-ray source applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873617
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  • 6
    Electronic Resource
    Electronic Resource
    Tungsten wire-array Z-pinch experiments at 200 TW and 2 MJ : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2105-2111 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Here Z, a 60 TW/5 MJ electrical accelerator located at Sandia National Laboratories, has been used to implode tungsten wire-array Z pinches. These arrays consisted of large numbers of tungsten wires (120–300) with wire diameters of 7.5 to 15 μm placed in a symmetric cylindrical array. The experiments used array diameters ranging from 1.75 to 4 cm and lengths from 1 to 2 cm. A 2 cm long, 4 cm diam tungsten array consisting of 240, 7.5 μm diam wires (4.1 mg mass) achieved an x-ray power of ∼200 TW and an x-ray energy of nearly 2 MJ. Spectral data suggest an optically thick, Planckian-like radiator below 1000 eV. One surprising experimental result was the observation that the total radiated x-ray energies and x-ray powers were nearly independent of pinch length. These data are compared with two-dimensional radiation magnetohydrodynamic code calculations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872881
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  • 7
    Electronic Resource
    Electronic Resource
    Titanium K-shell x-ray production from high velocity wire array implosions on the 20-MA Z accelerator : 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. 2081-2088 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The advent of the 20-MA Z accelerator [R. B. Spielman, C. Deeney, G. A. Chandler et al., Phys. Plasmas 5, 2105 (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z pinch K-shell scaling theories. The 2 cm long titanium arrays, which were mounted on a 40 mm diameter, produced between 75±15 to 125±20 kJ of K-shell x rays. A mass scan indicates that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7±0.1 to 3.2±0.2 keV and obtained a K-shell emission mass participation of up to 12%. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873461
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Computational investigation of single mode vs multimode Rayleigh–Taylor seeding in Z-pinch implosions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 4183-4198 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of two-dimensional magnetohydrodynamic calculations have been carried out to investigate single and multimode growth and mode coupling for magnetically-driven Rayleigh–Taylor instabilities in Z pinches. Wavelengths ranging from 5.0 mm down to 1.25 mm were considered. Such wavelengths are comparable to those observed at stagnation using a random density "seeding" method. The calculations show that wavelengths resolved by less than 10 cells exhibit an artificial decrease in initial Fourier spectrum amplitudes and a reduction in the corresponding amplitude growth. Single mode evolution exhibits linear exponential growth and the development of higher harmonics as the mode transitions into the nonlinear phase. The mode growth continues to exponentiate but at a slower rate than determined by linear hydrodynamic theory. In the two and three mode case, there is clear evidence of mode coupling and inverse cascade. In addition, distinct modal patterns are observed late in the implosion, resulting from finite shell thickness and magnetic field effects. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873153
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  • 10
    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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