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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4917-4928 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate modeling of load behavior in Z-pinch plasma radiation sources driven by high-current generators requires the measurement of fast-rise-time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B-dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by high dI/dt. In this paper, we describe the use of large-signal, nanosecond-time-resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressure B2/2μ0=μ0I2/8π2r2 generated at radius r by a current I flowing in a radial transmission line. Current measurements have been performed at radius r=2.54×10−2 m on Sandia National Laboratories' Proto-II (10 TW) and SATURN (30 TW) gas puff Z-pinch experiments with maximum currents of 10.1 MA and dI/dt to 2.1×1014 A/s. Comparisons with Faraday rotation and B-dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y-cut lithium niobate stress gauge on a pure tungsten electrode, current densities up to I/2πr=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X-cut quartz piezoelectric element and a tungsten-sapphire electrode impedance stack.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Particle Beam Fusion Accelerator II is a light-ion fusion accelerator that is presently capable of irradiating a 6-mm-diam sphere with ∼50 kJ of 5.5-MeV protons in ∼15 ns. An array of particle and x-ray diagnostics fielded on proton Inertial Confinement Fusion target experiments quantifies the incident particle beam and the subsequent target response. An overview of the ion and target diagnostic setup and capabilities will be given in the context of recent proton beam experiments aimed at studying soft x-ray emission from foam-filled targets and the hydrodynamic response of exploding-pusher targets. Ion beam diagnostics indicate ∼100 kJ of proton beam energy incident within a 1.2-cm radius of the center of the diode with an azimuthal uniformity which varied between 6% and 29%. Foam-filled target temperatures of 35 eV and closure velocities of 4 cm/μs were measured.
    Type of Medium: Electronic Resource
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  • 3
    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
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1519-1527 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fast Z-pinch implosions can efficiently convert the stored electrical energy in a pulsed-power accelerator into x rays. These x rays are produced when an imploding cylindrical plasma, driven by the magnetic field pressure associated with very large axial currents, stagnates upon the cylindrical axis of symmetry. On the Saturn pulsed-power accelerator [R. B. Spielman et al., in Proceedings of the 2nd International Conference on Dense Z Pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3] at Sandia National Laboratories, for example, currents of 6–8 MA with a rise time of less than 50 ns are driven through cylindrically symmetric loads, producing implosion velocities as high as 108 cm/s and x-ray energies exceeding 400 kJ. Hydromagnetic Rayleigh–Taylor instabilities and cylindrical load symmetry are critical, limiting factors in determining the assembled plasma densities and temperatures, and thus in the x-ray energies and pulse widths that can be produced on these accelerators. In recent experiments on the Saturn accelerator, these implosion nonuniformities have been minimized by using wire arrays with as many as 192 wires. Increasing the wire number produced significant improvements in the pinched plasma quality, reproducibility, and x-ray output power. X-ray pulse widths of less than 5 ns and peak powers of 75±10 TW have been achieved with arrays of 120 tungsten wires. Similar loads have recently been fielded on the Particle Beam Fusion Accelerator (PBFA II), producing x-ray energies in excess of 1.8 MJ at powers in excess of 160 TW. These intense x-ray sources offer the potential for performing many new basic physics and fusion-relevant experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Saturn pulsed power accelerator [R. B. Spielman et al., in Proceedings of the 2nd International Conference on Dense Z-pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3] at Sandia National Laboratories (SNL) and the Nova laser [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)] at Lawrence Livermore National Laboratory (LLNL) have been used to explore techniques for studying the behavior of ablator material in x-ray radiation environments comparable in magnitude, spectrum, and duration to those that would be experienced in National Ignition Facility (NIF) hohlraums [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)]. The large x-ray outputs available from the Saturn pulsed-power-driven z pinch have enabled us to drive hohlraums of full NIF ignition scale size at radiation temperatures and time scales comparable to those required for the low-power foot pulse of an ignition capsule. The high-intensity drives available in the Nova laser have allowed us to study capsule ablator physics in smaller-scale hohlraums at radiation temperatures and time scales relevant to the peak power pulse for an ignition capsule. Taken together, these experiments have pointed the way to possible techniques for testing radiation-hydrodynamics code predictions of radiation flow, opacity, equation of state, and ablator shock velocity over the range of radiation environments that will be encountered in a NIF hohlraum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 830-833 
    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
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A combination of a 400 ns, 300 mJ, 640 nm dye laser, and an optical streak camera have been used to demonstrate that time-resolved shadowgrams can be made of the implosion phase of tungsten wire arrays. Initial experiments have shown that mirror lifetime and spatial resolution are issues for this diagnostic technique. Nonetheless, these experiments have provided new information on wire array dynamics; specifically, they show that even with a 0.46 mm wire spacing, the high density regions formed by the wires, are separate until 30 ns into the main drive current. Peak currents of 6.6 MA were obtained 40 ns after the start of the current, while peak radiated powers of 85 TW were measured at 50 ns. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2677-2684 
    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
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5703-5706 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reliable sodium wire-array z-pinch load has been developed for use on the Saturn accelerator. This load routinely produces implosions with ≥200 GW of power in the heliumlike sodium 1s2–1s2p 1P1 line at 11 A(ring). Our best shots have used a 12.5-mm-diam, 20-mm-long annular array of 16 75-μm-diam pure sodium wires. This load will allow us to test predictions of gain in the sodium/neon resonant photoexcitation x-ray laser system.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recent experiments were performed at PBFA II to characterize the ion beam on-axis. The targets were comprised of two parts. One was a conical gold foil whose beam-induced fluorescence was used to obtain a beam footprint and a measurement of beam voltage. The gold also served as a Rutherford scattering source for an ion pinhole camera. The other part was an on-axis Li cylinder, contained within the gold cone, whose gamma output was used as a beam calorimeter. We present the results of this data.
    Type of Medium: Electronic Resource
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