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  • 1
    Digitale Medien
    Digitale Medien
    A cryogenic fiber maker for continuous extrusion (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2365-2368 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A cryogenic fiber maker that continuously extrudes fibers is presented. The design of the fiber maker is based on the use of two cooling stages maintained at different temperatures. The fiber maker consists of two copper reservoirs that are connected in series and are kept at different temperatures. The first reservoir is used to liquefy the gas coming in from an external gas line. The second reservoir is colder than the first; here, the liquid that comes from the first reservoir is frozen and later extruded using the pressure of the external line gas supply. A two-stage closed-cycle refrigerator (a Gifford–McMahon cooler), which uses helium as a working fluid, is used as a cooling system. The frozen gas is extruded through a stainless-steel capillary nozzle with internal diameters between 50 and 250 μm and a length of 2 mm. The temperature of the two reservoirs is set independently, which permits the extrusion rate of the fibers to be controlled and to produce the fibers continuously. Using this system, hydrogen, deuterium, nitrogen, and argon fibers of various diameters were extruded. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148945
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  • 2
    Digitale Medien
    Digitale Medien
    A novel technique for scintillator light collection in neutron measurements (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3034-3035 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In time resolved measurements of neutron emission, the most common practice is to use a plastic scintillator coupled to a fast photomultiplier. There are different ways of coupling the light emitted by the scintillator to the photomultiplier (PM), according to the size and the shape of the scintillator. Some of the more usual coupling geometries are light pipes, Plexiglas cones with silvered walls or mirror "huts'' facing the PM window.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1144600
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  • 3
    Digitale Medien
    Digitale Medien
    Investigation of the plasma jet formation in X-pinch plasmas using laser interferometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5140-5147 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A two-frame Mach–Zender interferometer is used to investigate the dynamics of X pinches formed from two 10 μm aluminum wires at current levels of 100 kA. Particularly, the columns of plasma that form on the interelectrode axis of the X pinch are studied quantitatively. It is demonstrated that the plasma which forms these columns does not come solely from expansion of the corona from the limbs of the X pinch but rather predominantly from the crossing point region. The results suggest that the plasma column is indeed a jet which consists of several components. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1321317
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  • 4
    Digitale Medien
    Digitale Medien
    Coronal plasma behavior of the Z pinch produced from carbon and cryogenic deuterium fibers (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3366-3372 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A series of fiber pinch experiments has been carried out on the MAGPIE (mega-ampere generator for plasma implosion experiments) generator (1.8 MA, 150 ns) [Mithell et al., Rev. Sci. Instrum. 67, 1533 (1996)] to study the temporal evolution of the coronal plasma. Analysis of schlieren photographs, axial streak images and gated x-ray photographs gives the radial and axial motion of the coronal plasma. The influence of a current pulse (prepulse) of 30 kA applied 200 ns before the main discharge was also studied. Radial expansion velocities of 5.5×106 cm/s for carbon fiber shots without prepulse and 3.6×106 cm/s for carbon fibers with prepulse were measured. Axial wavelengths (λz) of dominant instabilities in the corona were between 0.05 and 0.2 cm corresponding to ka∼10–20. Comparison of the results obtained with carbon fibers with and without current prepulse and cryogenic deuterium fibers are presented. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873050
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  • 5
    Digitale Medien
    Digitale Medien
    Two-dimensional magneto-hydrodynamic modeling of carbon fiber Z-pinch experiments (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4309-4317 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A two-dimensional magneto-hydrodynamic simulation incorporating cold start conditions is used to explain the early phase of carbon fiber Z-pinch experiments. The rapid development of large scale, nonlinear m=0 perturbations in the plasma corona is reproduced. X-ray bright spot formation in the necks of the instability is followed by bright spot bifurcation and fast axial motion. Bright spot bifurcation is found to be due to axial components of the j×B force and occurs off-axis due to the presence of a residual core of unionized carbon. Artificial diagnostic images are generated from the simulations data to allow direct comparison with experimental x-ray imaging and laser probing diagnostics. The accurate reproduction of the experimental images provides confirmation that the experimentally observed features are a repercussion of the non-linear development of the m=0 instability in an ionizing medium. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872593
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  • 6
    Digitale Medien
    Digitale Medien
    The dynamics of wire array Z-pinch implosions : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2016-2022 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Wire array Z-pinch dynamics are studied in experiments with 16-mm diameter arrays of between 8 and 64, 15-μm diameter aluminum wires, imploded in 200–260 ns by a 1.4-MA current pulse. Side-on laser probing shows early development of noncorrelated m=0-like instabilities with an axial wavelength ∼0.5 mm in individual wires. End-on interferometry (r-θ plane) shows azimuthal merging of the plasma with a density of 1017 cm−3 in 90–65 ns for 8–64 wires, respectively. At the same time low-density plasma reaches the array axis and forms a precursor pinch by 120–140 ns. At 0.7–0.85 of the implosion time a global m=0 instability with a wavelength of 1.7–2.3 mm was detected in soft x-ray gated images, laser probing, and optical streaks. The time when the instability reaches the observable level corresponds to the number of e-foldings for the growth of the classical Rayleigh–Taylor instability of ∫γ dt∼5.6–7. The scaling of this number with the number of wires is consistent with the instability growth from the seed level determined by the averaging of uncorrelated density perturbations in individual wires. Preliminary results from a 4×4 array permit the simultaneous observation by laser probing of the characteristic bubble and spike structure of the magneto Rayleigh–Taylor instability. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873456
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  • 7
    Digitale Medien
    Digitale Medien
    Time-resolved energy measurement of electron beams in fiber Z-pinch discharges (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 490-492 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The emission of hard x rays with energies much greater than the applied anode-cathode voltage is a common feature of Z-pinch plasmas. Here time-resolved measurements of such emission from fiber Z pinches at the mega-ampere current level are reported. The x-ray spectrum measured by an array of detectors is used to calculate the energy of the electron beam producing the emission. Pulses of between 20 and 100 ns duration were observed and electron-beam energy measurements of around 2 MeV obtained. It is thought that these high-energy beams are generated by the plasma becoming resistive at the time of x-ray emission. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872107
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  • 8
    Digitale Medien
    Digitale Medien
    Observations of plasma dynamics in the vacuum spark (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3910-3916 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental observations are presented of a vacuum spark driven by a low impedance pulse forming line delivering 100 kA to the load. A pulsed laser is used to form a preionizing plasma on the cathode. The combination of axial and radial optical streak camera observations, together with the time and space resolved soft x-ray emission, permit the evolution of the plasma dynamics, density and temperature to be measured. Three kinds of behavior are observed according to axial position. A close correlation is found between the x-ray and the optical emission, with the observation of micropinch formation. A discussion is presented in which the behavior of the vacuum spark under differing operating conditions is compared. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871020
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872444
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  • 10
    Digitale Medien
    Digitale Medien
    Optical probing of fiber z-pinch plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 682-691 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An experimental study of optical probing of a dense z-pinch plasma using the MAGPIE (mega-ampere generator for plasma implosion experiments) generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)] is reported. The generator was operated with a peak current of 1.1 MA rising in 150 ns (10%–90%). The loads were 33 μm diam carbon fibers. Faraday rotation was used to investigate the distribution of the current flowing in the plasma. A measurable Faraday rotation angle was observed only in a time window from 50 to 60 ns after the current start, due to the fact that this effect depends on a combination of the magnetic-field strength and electron number density. A new type of self-referencing cyclic radial shear interferometer was used to evaluate the plasma density profiles which are necessary for the reconstruction of the current distribution. It was calculated that ∼110 kA was flowing in the plasma at 52 ns after the current start. Shadowgraphy was used to study the dynamics of the plasma and to investigate the formation of instabilities. Plasma instabilities were observed at very early times (∼5 ns). These instabilities appeared to be not entirely axi-symmetric implying the existence of m=1 and maybe higher modes as well as m=0. The perturbations increased with time and evolved into density islands (isolated plasma fragments) distributed along the axis at late times (∼70 ns). © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872778
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