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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Aluminum wire array, Z-pinch experiments have been performed on an 8 MA generator using arrays consisting of 24, 30, and 42 wires. These experiments were designed to scan through a region of (array mass, implosion velocity) space in which greater than 30% conversion of the implosion kinetic energy into K-shell x rays was predicted to occur [Thornhill et al., Phys. Plasmas 1, 321 (1994)]. Array masses between 120 and 2050 μg/cm were used in these experiments. An analysis of the x-ray data taken using 24 wire arrays, shows a one-to-one correspondence between the observed kilo-electron-volt yields (5–64 kJ) and the fraction of initial array mass (0.3%–60%) that is radiating from the K shell. The 30 and 42 wire experiments demonstrated that tighter pinches with increased radiated powers were achieved with these larger wire number, improved symmetry arrays. In addition, increases in the implosion mass and array diameter in the 30 and 42 wire number cases resulted in increases in the radiated yield over the corresponding 24 wire shots, up to 88 kJ, which can be interpreted as due to improved coupling and thermalization of the kinetic energy. Moreover, spectroscopic analyses of the 30 and 42 wire experiments have shown that the increased wire numbers also resulted in K-shell radiating mass fractions of greater than 50%. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the concept of the dynamic hohlraum an imploding Z pinch is optically thick to its own radiation. Radiation may be trapped inside the pinch to give a radiation temperature inside the pinch greater than that outside the pinch. The radiation is typically produced by colliding an outer Z-pinch liner onto an inner liner. The collision generates a strongly radiating shock, and the radiation is trapped by the outer liner. As the implosion continues after the collision, the radiation temperature may continue to increase due to ongoing PdV (pressure times change in volume) work done by the implosion. In principal, the radiation temperature may increase to the point at which the outer liner burns through, becomes optically thin, and no longer traps the radiation. One application of the dynamic hohlraum is to drive an ICF (inertial confinement fusion) pellet with the trapped radiation field. Members of the dynamic hohlraum team at Sandia National Labs have used the pulsed power driver Z (20 MA, 100 ns) to create a dynamic hohlraum with temperature linearly ramping from 100 to 180 eV over 5 ns. On this shot zp214 a nested tungsten wire array of 4 and 2 cm diam with masses of 2 and 1 mg imploded onto a 2.5 mg plastic annulus at 5 mm diam. The current return can on this shot was slotted. It is likely the radiation temperature may be increased to over 200 eV by stabilizing the pinch with a solid current return can. A current return can with nine slots imprints nine filaments onto the imploding pinch. This degrades the optical trapping and the quality of the liner collision. A 1.6 mm diam capsule situated inside this dynamic hohlraum of zp214 would see 15 kJ of radiation impinging on its surface before the pinch itself collapses to a 1.6 mm diam. Dynamic hohlraum shots including pellets were scheduled to take place on Z in September of 1998. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Low density agar and aerogel foams were tested as z-pinch loads on the Saturn accelerator to study current flow initiation. In these first experiments, we studied the initial plasma conditions by measuring the visible emission at early times with a framing camera and a streaked one-dimensional imaging system. Later, near the stagnation when the plasma is hotter, x-ray imaging and spectral diagnostics were used to characterize the plasma. Filamentation and arcing at the current contacts were observed. Bright implosion features were also observed. Increasing the early time conductivity, by coating the target with a high-z layer and by providing a low-current prepulse, is the most important factor in obtaining good coupling to the machine. None of the pinches were uniform along the z axis. The prime causes of these problems are believed to be the electrode contacts and the current return configuration. Solutions are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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