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  • 1
    Electronic Resource
    Electronic Resource
    Improved flash γ-ray uniformity using a Bθ lens diode (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1406-1408 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significantly improved spatial uniformity of bremsstrahlung radiation, relative to a planar-anode diode, is obtained on the 3-MV, 150-kA HELIA accelerator when a Bθ lens diode is used to actively control the high-power electron beam at the exit of a coaxial, magnetically insulated transmission line. The advantage of this diode over other diodes which only passively control the beam is that better radiation uniformity for less beam loss is possible. Measurements taken on HELIA are shown to agree with theoretical expectations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100681
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  • 2
    Electronic Resource
    Electronic Resource
    Very intense pulsed electron beam (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 569-576 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An intense beam of pulsed electrons has been developed using the extended planar-anode diode to extract and focus the HERMES-III beam in a low-pressure gas cell without anode destruction. Measurements and a simulation model are compared and found in good agreement for focal lengths of ∼7–8 cm. They show that with this source a peak dose (peak dose rate) ∼200 J/g (8×1014 rad/s) in graphite can be generated with useful areas of 70 cm2. For the shorter focal length of ∼11 cm, the model predicts that a peak dose (peak dose rate) of 3800 J/g (1.5×1016 rad/s) can be generated over an area of 5 cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357114
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  • 3
    Electronic Resource
    Electronic Resource
    Voltage dependence of electron dynamics in high-power extended planar-anode diodes (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2004-2014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements confirm the ability of a numerical model to simulate basic features of electron flow and subsequent radiation output from EPA (extended planar-anode) diodes on HERMES III. HERMES III is a 19 MV, 700 kA, 25 ns electron accelerator. These diodes simultaneously terminate a coaxial MITL (magnetically insulated transmission line), and produce intense bursts of bremsstrahlung. The measurements and modeling show that (a) the EPA diode provides an impedance match to the MITL, (b) parapotential flow theory and the range of H− ions generated at the cathode can be used to measure the time-dependent voltage pulse and peak voltage VP, respectively, and (c) that ∼95% of the electrical energy transmitted to the diode can be converted to kinetic energy of electrons incident on bremsstrahlung targets. Further, it is demonstrated that the forward radiation fluence can be described by DA/Q=(76±11)V˜1.61 over the VP range 13–19 MV. DA, Q, and V˜ refer to the forward radiation fluence measured in Mrad(CaF2) cm2, the incident charge measured in C, and the median current-weighted accelerating voltage measured in MV, respectively. The dependence on VP of the beam characteristics at the targets is shown and the detailed kinetic-energy distribution there is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353166
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  • 4
    Electronic Resource
    Electronic Resource
    Compound-lens injector for a pulsed 13-TW electron beam (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8607-8614 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A robust injector capable of controlling the radius and angle of incidence of the pulsed, intense, annular electron beam extracted from the HERMES III accelerator is described. The injector, called the compound lens, uses a tapered anode to control the beam electrostatically, followed by a gas cell with externally applied current to control the beam magnetically. Adjustment of the anode-cathode gap and external current of the injector permits the radius and angle to be defined independently of one another. Measurements of these quantities confirm model expectations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353391
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  • 5
    Electronic Resource
    Electronic Resource
    Improved flash x-ray uniformity at 19 MeV using a compound-lens diode (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7283-7286 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significantly improved spatial uniformity of bremsstrahlung radiation, relative to a planar-anode diode, is obtained on the HERMES III accelerator when a compound-lens diode is used to control the 19-MeV, 700-kA electron beam. The compound-lens diode uses a conical anode to control the beam electrostatically, followed by a gas cell with externally applied current to control the beam magnetically. Variation of the external current enables average doses at the target to be varied by a factor of 3 without breaking the vacuum system of the accelerator to change diode hardware.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347626
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of electron flow in extended planar-anode diode operating at 19 MV and 700 kA (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1700-1711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron flow in a planar-anode diode having an extended anode-cathode gap operating on the HERMES III accelerator is characterized and compared with predictions of a computational model. The model combines a particle-in-cell code with Monte Carlo radiation transport. The comparisons confirm the model and show that the diode provides both a matched load and a versatile large-area source of γ rays for the study of nuclear radiation effects. Electrical and spatial parameters of the beam at the diode and the downstream radiation fields from a graphite target are presented as a function of the anode-cathode gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345640
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of a 700-kA 19-MeV electron beam in a short gas cell (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 472-482 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport of the Hermes III annular, 19-MeV, 700-kA, 25-ns, electron beam of radius (approximately-less-than)26 cm and current density (approximately-greater-than)0.4 kA/cm2, through short gas cells filled with N2, is characterized as a function of injection parameters, cell length, and gas pressure. These measurements are compared with predictions of numerical and analytical models. The comparisons confirm the main features of the models and show that the early-time behavior of the beam and gas ionization determines the net current and associated magnetic fields for the entire pulse, particularly at low pressure. The net current is minimized for pressures near 3 Torr and is 4%–7% of the injected current at peak power. Owing to the radial distribution of the net current density, the mean beam trajectory is effectively ballistic at this pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350680
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Symmetric aluminum-wire arrays generate high-quality Z pinches at large array radii (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3755-3763 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Saturn-accelerator study of annular, aluminum-wire array, Z-pinch implosions, in the calculated high-wire-number plasma-shell regime [Phys. Rev. Lett. 77, 5063 (1996)], shows that the radiated x-ray pulse width increases from about 4 nsec to about 7 nsec, when the radius of the array is increased from 8.75 to 20 mm at a fixed array mass of 0.6 mg. Eulerian radiation- magnetohydrodynamic code (E-RMHC) simulations in the r-z plane suggest that this pulse-width increase with radius is due to the faster growth of the shell thickness (that arises from a two-stage development in the magnetic Rayleigh–Taylor instability) relative to the increase in the shell implosion velocity. Over the array radii explored, the measured peak total x-ray power of ∼40 TW and energy of ∼325 kJ show little change outside of a ±15% shot-to-shot fluctuation and are consistent with the E-RMHC simulations. Similarly, the measured peak K-shell (lines plus continuum) power of ∼8 TW and energy of ∼70 kJ show little change with radius. The minimal change in K-shell yield is in agreement with simple K-shell radiation scaling models that assume a fixed radial compression for all initial array radii. These results suggest that the improved uniformity provided by the large number of wires in the initial array reduces the disruptive effects of the Rayleigh–Taylor instability observed in small-wire-number imploding loads. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872985
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  • 10
    Electronic Resource
    Electronic Resource
    Numerical simulations of annular wire-array z-pinches in (x,y), (r,θ), and (r,z) geometries (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2997-3005 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Total Immersion Particle [B. M. Marder, Math. Comput. 29, 434 (1973)] code has been used in several two-dimensional geometries to understand better the measured dynamics of annular, aluminum wire-array z-pinches. The areas investigated include the formation of the plasma sheath from current-induced individual wire explosions, the effects of wire number and symmetry on the implosion dynamics, and the dependence of the Rayleigh–Taylor instability growth on initial sheath thickness. A qualitative change in the dynamics with increasing wire number was observed, corresponding to a transition between a z-pinch composed of nonmerging, self-pinching individual wires, and one characterized by the rapid formation and subsequent implosion of a continuous plasma sheath. A sharp increase in radiated power with increasing wire number has been observed experimentally near this calculated transition. Although two-dimensional codes have correctly simulated observed power pulse durations, there are indications that three-dimensional effects are important in understanding the actual mechanism by which these pulse lengths are produced. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873024
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