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  • 1
    Electronic Resource
    Electronic Resource
    Terawatt fiber pinch experiments (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7261-7272 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pinch formation in fiber pinch experiments has been investigated in the lower terawatt regime. The main results are: (1) there are upper limits of breakdown voltage (∼700 kV) and current rise rate (∼20 kA/ns) beyond which leak discharges develop within the vacuum feed of the pulseline KALIF; (2) there is a lower limit of fiber radius (∼10 μm) below which pinch disruptions take place at a pinch current of (approximately-greater-than)300 kA; (3) the hot (Te≤1 keV) inhomogeneous pinch plasma develops typically 10 ns after local collapses (micropinches) at a pinch current (approximately-greater-than)400 kA and lives for more than 50 ns; (4) neutron emission (yield of CD2 fibers ∼1010) appears mostly isotropic; (5) all fiber pinches show global expansion with velocities reaching from typically 10 μm/ns (initial expansion) to (approximately-greater-than)100 μm/ns; and (6) the power requirements for the fiber ablation process are contradictory to those for the final pinch phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349773
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  • 2
    Electronic Resource
    Electronic Resource
    Observations of soft x-ray production in the speed 2 plasma focus (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 613-617 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new soft x-ray source has been developed and investigated. Argon is injected into a plasma focus through a hole in the anode. The pinch emits several Joules per shot of soft x rays at λ〈0.5 nm from multiple micropinches well aligned along the axis of symmetry. When viewed end-on the pinch appears as a small source of 700 μm diam. The micropinches have the following characteristics: Range of size 40–250 μm (depending on radiation wavelength), density 1028 m−3, temperature 1.5 keV, and lifetime typically less than 1 ns. The helium-like emission from single micropinches lasts for 250 ps only, which is much shorter than previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347394
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  • 3
    Electronic Resource
    Electronic Resource
    The dynamics of bifurcating bright-spots in fiber Z-pinch plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2967-2971 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented from the diagnosis of the optical and x-ray emission from "bright-spots" in carbon fiber Z-pinch experiments using the MAGPIE (Mega-Ampere Generator for Plasma Implosion Experiments) generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]. Inhomogeneities evolve very rapidly within the plasma with bright-spots becoming detectable after 15–20 ns. After a short (∼4 ns) duration formation phase, these bright-spots exhibit highly dynamic behavior. Bifurcation of the bright-spots is observed giving rise to rapid axial motion at 1–3×105 ms−1. The post-bifurcation bright-spots persist for up to 40 ns. Analysis of cross-filtered, time integrated, x-ray pinhole images yield bright-spot parameters during the formation phase (diameter ∼80 μm, temperature 250–300 eV, ion number densities ∼2×1026 m−3). With a spatial resolution of 175 μm, the strong temperature and density gradients within the post-bifurcation spots can be resolved in gated x-ray images with 2 ns exposure times. After the dynamic phase of bright-spot evolution, the pinch enters a quiescent phase where the time scale for evolution is much longer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872444
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  • 4
    Electronic Resource
    Electronic Resource
    Optimization of a high-voltage trigatron switch (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3659-3663 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Work has been carried out to optimize the operation of a high-voltage trigatron switch. It is demonstrated here that the trigatron can operate in two different modes depending on the route of the initial breakdown. This initial breakdown can occur either to the adjacent electrode or to the opposite electrode. It is shown here that, for a given switch, the mode of operation depends only on the ratio of trigger voltage to working voltage. The optimization was based upon the suggestion that the optimum operation of a trigatron would occur when the trigger pin breaks down simultaneously to both the adjacent and the opposite electrodes. This occurs for the trigger to working voltage ratio, which results in equal mean electric fields across the main gap and the trigger gap. The experiments were carried out with working voltages, Vg, between −1 and −2 MV and with trigger voltage to working voltage ratios of between −2% and −8%. It is shown that the minimum delay and jitter figures are indeed obtained with the trigger voltage closest to this optimum value, Vt*. For the switch used here, this corresponded to a ratio of Vt*/Vg=−3.4%. A single switch was operated for two hundred shots with a working voltage of −2 MV and the optimum trigger voltage and gave an average delay of 44 ns with an overall jitter of 4.4 ns. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359943
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  • 5
    Electronic Resource
    Electronic Resource
    A high impedance mega-ampere generator for fiber z-pinch experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1533-1541 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: At Imperial College a mega-ampere generator for plasma implosion experiments has been designed, built, and commissioned. With a final line impedance of 1.25 Ω this terawatt class generator has been designed primarily to drive a maximum current of 1.8 MA with a rise time of 150 ns into high inductance z-pinch loads of interest to radiative collapse studies. This article describes the design and tests of the generator which has a novel configuration of lines and a new design of a magnetically insulated transmission line (MITL). In summary, the generator consists of four Marx generators each of the Hermes III type (2.4 MV, 84 kJ), each connected to 5 Ω pulse forming lines and trigatron gas switches. The power is fed into the matched 1.25 Ω vertical transfer line which feeds a diode stack and a short conical MITL in vacuum which concentrates the power into the z-pinch load. At 80% charge a current rising to 1.4 MA in 150 ns has been measured in a 15 nH inductive short. Similar results are obtained when using a plasma load. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146884
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of the source of inorganic nitrogen on growth and enzymes of nitrogen assimilation in soybean and wheat cells in suspension cultures (1972)
    Springer
    Planta 105 (1972), S. 15-24 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Soybean (Glycine max L. cv. Mandarin) and wheat (Triticum monococcum L.) cells were grown in media with NO3 - plus NH4 + (B5) and NO3 - without NH4 + (B5-NH4) as nitrogen sources. Changes in pH, [NO3 -] and [NH4 +] in media, and dry weight, protein content, nitrate reductase (NR) and glutamate dehydrogenase (GDH) in the cells were followed for about 170 h. With both NH4 + and NO3 - in the medium, NH4 + was utilized very quickly. Soybean cells grew poorly in the absence of NH4 + while wheat cells grew equally well on media with or without NH4 +. When soybean cells were grown in medium with NO3 - plus NH4 +, dry weight and NR activity remained relatively low for several hours after which both increased rapidly. This coincided with the time NH4 + was depleted from the medium. In the absence of NH4 +, soybean cell growth and NR activity remained low. NR activity in wheat cells, and GDH activity in soybean and wheat cells, did not vary significantly in the presence or absence of NH4 +.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385159
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  • 7
    Electronic Resource
    Electronic Resource
    The ability of amino compounds and conditioned medium to alleviate the reduced nitrogen requirement of soybean cells grown in suspension cultures (1972)
    Springer
    Planta 105 (1972), S. 25-32 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Various nitrogen compounds were tested for their ability to alleviate the reduced nitrogen requirement of soybean cells growing in defined liquid medium containing nitrate as the alternative nitrogen source. Either l-glutamine, l-alanine, putrescine or NH4 + satisfied this requirement. Addition of l-glutamate resulted in poor growth. Where growth was stimulated, nitrate reductase (NR) activity increased whereas glutamate dehydrogenase activity in the cells showed no such correlation. In all fresh media which supported rapid growth, NR activity first decreased rapidly to a low value. Subsequent dry weight increases occurred concommitantly with an increase in NR activity. When 2,4-dichlorophenoxyacetic acid was omitted from the medium the growth was slow and the NR activity did not increase. During the first 40 h of incubation in medium containing NH4 + plus NO3 - the cells produced a growth-enhancing factor(s). This factor(s) was present in the cells and in the medium and eliminated the requirement for reduced nitrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385160
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