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  • 1
    Electronic Resource
    Electronic Resource
    Electron–anode interactions in particle-in-cell simulations of applied-B ion diodes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3369-3387 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle-in-cell simulations of applied-B ion diodes using the QUICKSILVER code [D. B. Seidel et al., in Proceedings of the Europhysics Conference on Computational Physics, Amsterdam, 1990, edited by A. Tenner (World Scientific, Singapore, 1991), p. 475] have been augmented with Monte Carlo calculations of electron–anode interactions (reflection and energy deposition). Extraction diode simulations demonstrate a link between the instability evolution and increased electron loss and anode heating. Simulations of radial and extraction ion diodes show spatial nonuniformity in the predicted electron loss profile leading to hot spots on the anode that rapidly exceed the 350 °C–450 °C range, known to be sufficient for plasma formation on electron-bombarded surfaces. Thermal desorption calculations indicate complete desorption of contaminants with 15–20 kcal/mole binding energies in high-dose regions of the anode during the power pulse. Comparisons of parasitic ion emission simulations and experiment show agreement in some aspects, but also highlight the need for better ion source, plasma, and neutral gas models. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873576
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  • 2
    Electronic Resource
    Electronic Resource
    Three-dimensional, particle-in-cell simulations of applied-B ion diodes on the particle beam fusion accelerator II (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2079-2093 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used the three-dimensional, particle-in-cell code QUICKSILVER [J. P. Quintenz, et al., Lasers and Particle Beams 12, 283 (1994)] to simulate radial applied-B ion diodes on the particle beam fusion accelerator II at Sandia National Laboratories. The simulations agree well with experiments early in the beam pulse, but differ substantially as the ion-beam current increases. This is attributed to the oversimplified ion emission model. We see the same instabilities seen in earlier simulations with idealized diode geometries; Early in time there is a diocotron instability, followed by a transition to an "ion mode'' instability at much lower frequency. The instability-induced beam divergence for the ∼10 MeV beam during the diocotron phase is 〈10 mrad, significantly less than the total beam divergence in experiments early in the pulse, but increases to (approximately-greater-than)25 mrad after the transition. The ion mode has a distinct harmonic structure along the applied field lines, making the instability transition sensitive to the diode geometry. The ion mode instability in our latest simulations is consistent with evidence of instabilities from recent experiments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363100
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  • 3
    Electronic Resource
    Electronic Resource
    Charge exchange effects in ion diodes (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2879-2887 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new one-dimensional particle simulation code has been developed to investigate the effect of charge exchange between the ions and background neutrals in a planar anode-cathode gap. The code has been used to study the effect of beam ions charge exchanging with neutrals in the anode plasma in an ion diode. Charge exchange creates a fast neutral population which expands into the gap much faster than the anode plasma itself. This flux quickly increases the neutral density throughout the gap. Furthermore, multiple charge exchanges reduce the ion flux and mean energy, and broaden the ion beam energy distribution. A description of the code and quantitative results of these effects are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344193
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  • 4
    Electronic Resource
    Electronic Resource
    Simulations of magnetically insulated multistage ion diodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2072-2081 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytic theory for magnetically insulated multistage acceleration of high intensity ion beams has been presented [J. Appl. Phys. 67, 6705 (1990)]. This theory predicts an operating behavior that is strongly dependent on the electron density profile. A numerical investigation, using both two-dimensional (2-D) and three-dimensional (3-D) particle-in-cell codes, of multistage diode operating behavior is presented in this paper. The 2-D results are consistent with the analytic results based on a very thin electron sheath. In contrast, the 3-D simulations are consistent with the analytic theory based on a thick electron sheath. The different results are due to the growth of electromagnetic instabilities in the 3-D simulations, which generate fluctuations that broaden the electron sheath. The 2-D simulations did not properly model these instabilities because they propagate in the direction that was ignored. In addition to these results, the 3-D code was used to study the generation of ion divergence due to the instability induced fluctuations. These simulations show a positive correlation between the ion current density (normalized for space-charge effects) and the growth of transverse ion velocities during acceleration. It is found that, at low beam current densities, ion divergence can be reduced significantly by postacceleration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870602
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  • 5
    Electronic Resource
    Electronic Resource
    Three-dimensional particle-in-cell simulations of applied-B ion diodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 429-443 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The three-dimensional particle-in-cell code quicksilver [Seidel et al., Computational Physics, edited by A. Tenner (World Scientific, Singapore, 1991), p. 475] has been used to study applied-B ion diodes. The impedance behavior of the diode in these simulations is in good agreement with both analytic theory and experiments at peak power. The simulations also demonstrate the existence of electromagnetic instabilities which induce divergence in the ion beam. Early in time, there is an instability at high frequency relative to the ion transit time τi, and the resulting beam divergence is low. However, later in time, the system makes a transition to an instability with a frequency close to 1/τi, and the ion beam divergence rises to an unacceptably high value. The transition is associated with the build-up of electron space charge in the diode, and the resulting increase in the beam current density enhancement (J/JCL). Using different schemes to inhibit the electron evolution, the transition has both been postponed and permanently eliminated, resulting in Li+1 ion beams with a sustained divergence of ∼10 mrad at an energy of ∼10 MeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870844
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  • 6
    Electronic Resource
    Electronic Resource
    Ion divergence in magnetically insulated diodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2175-2182 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetically insulated ion diodes are being developed to drive inertial confinement fusion. Ion beam microdivergence must be reduced to achieve the very high beam intensities required to achieve this goal. Three-dimensional particle-in-cell simulations [Phys. Rev. Lett. 67, 3094 (1991)] indicate that instability-induced fluctuations can produce significant ion divergence during acceleration. These simulations exhibit a fast growing mode early in time, which has been identified as the diocotron instability. The divergence generated by this mode is modest, due to the relatively high-frequency ((approximately-greater-than)1 GHz). Later, a low-frequency low-phase-velocity instability develops with a frequency that is approximately the reciprocal of the ion transit time. This instability couples effectively to the ions, and can generate unacceptably large ion divergences ((approximately-greater-than)30 mrad). Linear stability theory reveals that this mode has structure parallel to the applied magnetic field and is related to the modified two-stream instability. Measurements of ion density fluctuations and energy-momentum correlations have confirmed that instabilities develop in ion diodes and contribute to the ion divergence. In addition, spectroscopic measurements indicate that lithium ions have a significant transverse temperature very close to the emission surface. Passive thin-film lithium fluoride (LiF) anodes have larger transverse beam temperatures than laser-irradiated active sources. Calculations of the ion beam source divergence for the LiF film due to surface roughness and the possible loss of adhesion and fragmentation of this film are presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871672
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  • 7
    Electronic Resource
    Electronic Resource
    Particle simulations of plasma and dielectric Cerenkov masers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 908-915 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new particle simulation model has been developed to investigate Cerenkov masers. The novel aspects of the code are briefly described, and results of simulations of two types of Cerenkov masers are presented. The first device uses a conventional dielectric lining as its slow-wave structure. The second is a new type of Cerenkov maser in which a circular waveguide is partially filled with a dense annular plasma instead of a dielectric layer. Both simulations agree well with experimental results and linear theory calculations. Saturation of the instability is shown to be due to trapping of the beam electrons. The relative merits of each system are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866774
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  • 8
    Electronic Resource
    Electronic Resource
    Particle-in-cell simulations of electron flow in the post-hole convolute of the Z accelerator (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4534-4544 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The three-dimensional, particle-in-cell code QUICKSILVER [J. P. Quintenz et al., Lasers Part. Beams 12, 283 (1994)] is now being used to simulate the inner region of the Z accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. The simulations model electron flow and anode losses in the double post-hole convolute, which couples four radial, magnetically insulated transmission lines (MITLs) in parallel to a single MITL that drives a Z-pinch load. To efficiently handle the large range in the magnetic field, 0〈B〈200 T, the particle pusher is modified to subcycle the electron advance relative to the field solver. Results from a series of simulations using a constant-impedance load are presented. The locations of electron losses to the anode in the convolute are in qualitative agreement with damage to the Z hardware. The electron energy deposited in these anode regions rapidly heats the surface to temperatures above 400 °C—the threshold at which anode plasma formation is expected. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1401118
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental configuration for isentropic compression of solids using pulsed magnetic loading (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 3587-3595 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A capability to produce quasi-isentropic compression of solids using pulsed magnetic loading on the Z accelerator has recently been developed and demonstrated [C. A. Hall, Phys. Plasmas 7, 2069 (2000)]. This technique allows planar, continuous compression of materials to stresses approaching 1.5 Mbar. In initial stages of development, the experimental configuration used a magnetically loaded material cup or disk as the sample of interest pressed into a conductor. This installation caused distortions that limited the ability to attach interferometer windows or other materials to the rear of the sample. In addition, magnetic pressure was not completely uniform over sample dimensions of interest. A new modular configuration is described that improves the uniformity of loading over the sample surface, allows materials to be easily attached to the magnetically loaded sample, and improves the quality of data obtained. Electromagnetic simulations of the magnetic field uniformity for this new configuration will also be presented. Comparisons between data on copper to ∼300 kbar using the old and new experimental configurations will also be made. Results indicate that to within experimental error, the configurations produce similar results in the pressure-volume plane. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1394178
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  • 10
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    Measurements of Acceleration Gap Dynamics in a 20-TW Applied-Magnetic-Field Ion Diode (1995)
    American Physical Society
    Details
    Publication Date: 1995-03-06
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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