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  • 1
    Electronic Resource
    Electronic Resource
    Power flow between a plasma-opening switch and a load separated by a high-inductance magnetically insulated transmission line (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2648-2656 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented from particle-in-cell simulations of the electron flow launched from a plasma opening switch (POS) into a magnetically insulated transmission line (MITL) as the POS opens. The opening process of the POS is treated by removing plasma from a fixed anode-cathode gap with an opening time of τrise. To be similar to opening switch experiments at Physics International, the simulations were performed with the same inductance LMITL between the POS and load. When LMITL/τrise is large compared to the POS flow impedance, this inductance effectively isolates the POS from the load during the opening process and the POS voltage is insensitive to changes in the load impedance. Analysis and simulations show that the peak load power is maximized when the load impedance is equal to the POS flow impedance. In contrast to previous theories and simulations of magnetically insulated flows, a large amount of electron flow in the MITL is concentrated near the anode. This is a result of the high effective impedance imposed on the POS by the inductive load which causes a significant electron current loss in the POS. As a result, many electrons lose insulation on the load side of the POS gap and those that do flow into the MITL have been accelerated to nearly the full POS potential. Electrons then E×B drift on equipotential lines close to the anode as they enter the MITL and flow toward the load. Current losses in the MITL are observed due to the proximity of the electron flow to the anode. Some electrons flow from the MITL directly into the load and are registered as load current while others E×B drift back toward the POS along the cathode surface. This is possible because the electron flow launched into the MITL from the POS is large enough to cause sufficient positive image charges on the cathode so that the electric field points out of the cathode surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358506
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray scattering using synchrotron radiation shows nitrite reductase from Achromobacter xylosoxidans to be a trimer in solution (1993)
    s.l. : American Chemical Society
    Biochemistry 32 (1993), S. 7360-7366 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00080a005
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation of collisional effects in the plasma erosion opening switch (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6646-6653 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 cm long. Current channels in the main body of the plasma have been observed that are more than 10 cm (or more than about 60 collisionless skin depths) wide. In addition, the maximum current carried by the switch before opening (the conduction current) seems to scale roughly linearly with plasma density n and switch length l. Collisionless pic code simulations of the plasma switch show current conducted in skin-depth-like channels, with the conduction current scaling close to l 2/5 and n1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring the pic simulations and experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly with l and as n1/2 in the anode-dominated case. In the cathode-dominated case, linear scaling with both length and density can be inferred from the cathode penetration distance versus time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342050
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  • 4
    Electronic Resource
    Electronic Resource
    Current channel migration and magnetic field penetration in a perfectly conducting plasma with emitting, conducting boundaries (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2307-2314 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In collisionless simulations of the plasma erosion opening switch, a highly conductive plasma allows magnetic field penetration through the entire length of the plasma, to depths almost two orders of magnitude greater than the collisionless skin depth, c/ωpe. Field penetration is accomplished by a narrow (skin-depth-like) current channel that migrates through the plasma. The plasma behind the current channel is unable to shield the rising magnetic field from the body of the plasma and allows it to penetrate almost instantly and completely through the plasma up to the current channel. The migration of the channel and the penetration of the field appear to occur in the absence of both Coulomb collisions and instabilities. These unusual features are permitted by the electric field structure in the plasma behind the current channel and the presence of conducting boundaries that can emit electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344287
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  • 5
    Electronic Resource
    Electronic Resource
    Charged particle flow in plasma-filled pinched-electron-beam diodes (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2274-2286 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma-filled pinched-electron-beam diode experiments have been performed on the Gamble II (1.5 MV, 800 kA, 60 ns) pulsed power generator at Naval Research Laboratory. These plasma-filled diode (PFD) experiments show three phases of behavior: a low impedance phase followed by a phase of rapidly increasing impedance that culminates in a relatively constant vacuum impedance phase. The duration of the low impedance phase as well as the final operating impedance depends on the prefill plasma density. The charged particle flow in the PFD is studied with one-dimensional (1-D) and two-dimensional (2-D) simulation models. These simulation models show the formation of growing sheaths at both electrodes during the low impedance phase. The end of the low impedance phase in the simulations coincides with the two sheaths meeting in the center of the anode-cathode (A-K) gap. Based on these observations, an analytic model was developed that treats the low impedance phase as symmetric bipolar sheaths. The analytical model adequately predicts the duration of the low impedance phase predicted by the 1-D simulation model. Differences between the bipolar model and the experiments or 2-D simulations can be explained in terms of magnetized sheaths which enhance the ion current over the bipolar level and cause the sheath to grow faster than the bipolar model. During the rapidly increasing impedance phase, the simulations show that the cathode sheath quickly expands to completely fill the A-K gap. At this time, charged particle flow in the simulation models are consistent with the vacuum gap spacing. Experimentally, the higher density, longer conduction time, PFD shots exhibited a significantly lower final impedances than predicted by 2-D simulations. This difference is probably caused by expanding electrode surface plasmas produced by the interaction of the plasma source with one or both electrode surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354711
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  • 6
    Electronic Resource
    Electronic Resource
    Gap formation processes in a high-density plasma opening switch (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 299-309 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A gap opening process in plasma opening switches (POS) is examined with the aid of numerical simulations. In these simulations, a high density (ne=1014–5×1015 cm−3) uniform plasma initially bridges a small section of the coaxial transmission line of an inductive energy storage generator. A short section of vacuum transmission line connects the POS to a short circuit load. The results presented here extend previous simulations in the ne=1012–1013 cm−3 density regime. The simulations show that a two-dimensional (2-D) sheath forms in the plasma near a cathode. This sheath is positively charged, and electrostatic sheath potentials that are large compared to the anode–cathode voltage develop. Initially, the 2-D sheath is located at the generator edge of the plasma. As ions are accelerated out of the sheath, it retains its original 2-D structure, but migrates axially toward the load creating a magnetically insulated gap in its wake. When the sheath reaches the load edge of the POS, the POS stops conducting current and the load current increases rapidly. At the end of the conduction phase a gap exists in the POS whose size is determined by the radial dimensions of the 2-D sheath. Simulations at various plasma densities and current levels show that the radial size of the gap scales roughly as B/ne, where B is the magnetic field. The results of this work are discussed in the context of long-conduction-time POS physics, but exhibit the same physical gap formation mechanisms as earlier lower density simulations more relevant to short-conduction-time POS. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871106
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  • 7
    Electronic Resource
    Electronic Resource
    Particle-in-cell simulations of fast magnetic field penetration into plasmas due to the Hall electric field (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3556-3563 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle-in-cell (PIC) simulations are used to study the penetration of magnetic field into plasmas in the electron-magnetohydrodynamic (EMHD) regime. These simulations represent the first definitive verification of EMHD with a PIC code. When ions are immobile, the PIC results reproduce many aspects of fluid treatments of the problem. However, the PIC results show a speed of penetration that is between 10% and 50% slower than predicted by one-dimensional fluid treatments. In addition, the PIC simulations show the formation of vortices in the electron flow behind the EMHD shock front. The size of these vortices is on the order of the collisionless electron skin depth and is closely coupled to the effects of electron inertia. An energy analysis shows that one-half the energy entering the plasma is stored as magnetic field energy while the other half is shared between internal plasma energy (thermal motion and electron vortices) and electron kinetic energy loss from the volume to the boundaries. The amount of internal plasma energy saturates after an initial transient phase so that late in time the rate that magnetic energy increases in the plasma is the same as the rate at which kinetic energy flows out through the boundaries. When ions are mobile it is observed that axial magnetic field penetration is followed by localized thinning in the ion density. The density thinning is produced by the large electrostatic fields that exist inside the electron vortices which act to reduce the space-charge imbalance necessary to support the vortices. This mechanism may play a role during the opening process of a plasma opening switch. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871946
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  • 8
    Electronic Resource
    Electronic Resource
    Hall magnetohydrodynamic modeling of a long-conduction-time plasma opening switch (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3444-3454 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of long-conduction-time (τc∼1 μs) plasma opening switches (POS) is studied using magnetohydrodynamic (MHD) theory, including the Hall term. Plasma switches with initial electron densities of ne=1014–1016 cm−3 are modeled; these densities are appropriate to recent experiments carried out at the Naval Research Laboratory using the Hawk generator (800 kA, 1.2 μs). The conduction times obtained from the simulation studies are in the range τc(approximately-equal-to)0.4–2.0 μs. The POS plasma is strongly redistributed by the penetrating magnetic field. As the field penetrates, it pushes the plasma both axially and radially (i.e., toward the anode and cathode). In the higher-density regime (ne(approximately-greater-than)1015 cm−3), Hall effects do not play a significant role. The magnetic field acts as a snowplow, sweeping up and compressing the plasma as it propagates through the POS plasma. In the lower-density regime (ne〈1015 cm−3), Hall effects become important in two ways: the conduction time is less than that expected from ideal MHD, and the POS plasma becomes unstable as the magnetic field penetrates, leading to finger-like density structures. The instability is the unmagnetized ion Rayleigh–Taylor instability and is driven by the magnetic force accelerating the plasma. The structuring of the plasma further decreases the conduction time and causes the penetrating magnetic field to have a relatively broad front in comparison to EMHD simulations (i.e., Vi=0). The simulation results are consistent with experimental data for conduction currents 300–800 kA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870493
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  • 9
    Electronic Resource
    Electronic Resource
    Plasma opening switch conduction scaling (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3893-3901 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma opening switch (POS) experiments performed on the Hawk generator [Commisso et al., Phys. Fluids B 4, 2368 (1992)] (750 kA, 1.2 μs) determine the dependence of the conduction current and conduction time on plasma density, electrode dimensions, and current rise rate. The experiments indicate that for a range of parameters, conduction is controlled by magnetohydrodynamic (MHD) distortion of the plasma, resulting in a low density region where opening can occur, possibly by erosion. The MHD distortion corresponds to an axial translation of the plasma center-of-mass by half the initial plasma length, leading to a simple scaling relation between the conduction current and time, and the injected plasma density and POS electrode dimensions that is applicable to a large number of POS experiments. For smaller currents and conduction times, the Hawk data suggest a non-MHD conduction limit that may correspond to electromagnetohydrodynamic (EMH) field penetration through the POS plasma. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871018
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of a microsecond-conduction-time plasma opening switch (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2368-2376 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents data and analyses from which emerges a physical picture of microsecond-conduction-time plasma opening switch operation. During conduction, a broad current channel penetrates axially through the plasma, moving it toward the load. Opening occurs when the current channel reaches the load end of the plasma, far from the load. During conduction, the axial line density in the interelectrode region is reduced from its value with no current conduction as a result of radial hydrodynamic forces associated with the current channel. A factor of 20 reduction is observed at opening in a small, localized region between the electrodes. When open, the switch plasma behaves like a section of magnetically insulated transmission line with an effective gap of 2 to 3 mm. Increasing the magnetic field in this gap by 50% results in an improvement of 50% in the peak load voltage and load current rise time, to 1.2 MV and 20 nsec, respectively. An erosion opening mechanism explains the inferred gap growth rate using the reduced line density at opening. Improved switch performance results when the maximum gap size is increased by using a rising load impedance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860207
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