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  • 1
    Electronic Resource
    Electronic Resource
    Time-resolved spectroscopic measurements of ∼1 keV, dense, subnanosecond X-pinch plasma bright spots : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2165-2172 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bright, ∼1 μm x-ray sources (micropinches) produced within exploding wire X pinches are found to be near solid density and ∼1 keV electron temperature. For example, with a Ti X pinch, a 90 ps lifetime, 1.5–1.8 keV electron temperature, ∼1023/cm3 electron density plasma was observed. These plasma characteristics were determined using time-resolved x-ray spectra produced by 2- and 4-wire X pinches and collected by an x-ray streak camera with 〈10 ps time resolution. Together with a spherically bent mica crystal spectrograph, the streak camera recorded the 1–10 keV radiation emitted from X pinches made from different wire materials. Some spectra were dominated by continuum and others by line radiation. Spectral features varied on time scales ranging from 10 to 300 ps, depending on the wire material. Results are presented that demonstrate the necessity of time-resolved data for determining plasma conditions from micropinch x-ray spectra. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1458587
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of discrete wires on the implosion dynamics of wire array Z pinches (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3734-3747 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A phenomenological model of wire array Z-pinch implosions, based on the analysis of experimental data obtained on the mega-ampere generator for plasma implosion experiments (MAGPIE) generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)], is described. The data show that during the first ∼80% of the implosion the wire cores remain stationary in their initial positions, while the coronal plasma is continuously jetting from the wire cores to the array axis. This phase ends by the formation of gaps in the wire cores, which occurs due to the nonuniformity of the ablation rate along the wires. The final phase of the implosion starting at this time occurs as a rapid snowplow-like implosion of the radially distributed precursor plasma, previously injected in the interior of the array. The density distribution of the precursor plasma, being peaked on the array axis, could be a key factor providing stability of the wire array implosions operating in the regime of discrete wires. The modified "initial" conditions for simulations of wire array Z-pinch implosions with one-dimension (1D) and two-dimensions (2D) in the r–z plane, radiation-magnetohydrodynamic (MHD) codes, and a possible scaling to a larger drive current are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385373
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  • 3
    Electronic Resource
    Electronic Resource
    Experiments measuring the initial energy deposition, expansion rates and morphology of exploding wires with about 1 kA/wire (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 216-230 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wire-array Z-pinch implosion experiments begin with wire heating, explosion, and plasma formation phases that are driven by an initial 50–100 ns, 0–1 kA/wire portion of the current pulse. This paper presents expansion rates for the dense, exploding wire cores for several wire materials under these conditions, with and without insulating coatings, and shows that these rates are related to the energy deposition prior to plasma formation around the wire. The most rapid and uniform expansion occurs for wires in which the initial energy deposition is a substantial fraction of the energy required to completely vaporize the wire. Conversely, wire materials with less energy deposition relative to the vaporization energy show complex internal structure and the slowest, most nonuniform expansion. This paper also presents calibrated radial density profiles for some Ag wire explosions, and structural details present in some wire explosions, such as foam-like appearance, stratified layers and gaps. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323759
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of insulating coatings on exploding wire plasma formation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 429-432 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Substantial increases are reported in the expansion rates of exploding, dense wire cores under conditions simulating the prepulse phase of wire array z-pinch experiments [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] using wires with insulating coatings. The insulation apparently allows additional wire heating by delaying the formation of plasma around the wires. Once plasma is formed it terminates significant current flow in the residual wire cores. This effect is demonstrated for 25-μm diameter W and 25-μm diameter Ag wires. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873825
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  • 5
    Electronic Resource
    Electronic Resource
    Evolution of the structure of the dense plasma near the cross point in exploding wire X pinches (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2840-2846 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of the dense plasma near the cross point of an X pinch has been investigated using 1 ns x-ray backlighting images at different moments relative to the start of 100 ns [full width at half maximum (FWHM)] 200 kA current pulses. If the two metal wires are fine enough (e.g., 10 μm W or 17.5 μm Mo) to form a pinch at the cross point, accompanied by an x-ray burst, with the available current pulse, then the images show three stages of development: a radial explosion/expansion phase; an implosion during which a dense Z pinch of 200–300 μm length forms at the cross point together with plasma jets which move axially away from that point; and a breaking up of the Z pinch, coincident in time with one or two x-ray bursts, after which a 300 μm gap opens up. For W, the backlighter minimum sensitivity is 1017/cm2 areal density, and the dense Z pinch is estimated to have a volume density close to 1021/cm3. Shock waves appear to be expanding at about 50 μm/ns from the end points of the collapsing Z pinch, where the plasma was the most dense. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873241
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  • 6
    Electronic Resource
    Electronic Resource
    Exploding aluminum wire expansion rate with 1–4.5 kA per wire (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1555-1563 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray backlighter images (radiographs) of current-induced explosions of 12.7–25 μm diam Al wires have been used to determine the expansion rate and internal structure of the dense wire cores. The current rises to 1–4.5 kA per wire in 350 ns, but voltage and current measurements show that the energy driving the explosion is deposited resistively during the first 40–50 ns, when the current is only a few hundred amperes per wire. A voltage collapse then occurs as a result of plasma formation around the wire, effectively terminating the energy deposition in the wire core. High-resolution radiographs obtained over the next 150–200 ns show the expanding wire cores to have significant axial stratification and foamlike structures with ∼10 μm scale lengths over most of the wire length before they disappear in the expansion process. The expansion rate of the portion of the wire cores that is dense enough to be detected by radiography is 1.4–2 μm/ns commencing approximately 25 ns after the moment of the voltage collapse. (The sensitivity limit is equivalent to 0.2 μm of solid density Al.) By 250 ns after the start of the current pulse, the detectable wire core diameter is 250 μm, but it contains only about 30% of the initial wire material. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873975
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  • 7
    Electronic Resource
    Electronic Resource
    Radiographic and spectroscopic studies of X-pinch plasma implosion dynamics and x-ray burst emission characteristics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1305-1318 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results are presented from studies of the dynamics of X-pinch plasmas, formed using two fine wires that cross and touch at a single point (in the form of an X) as the load of a high current pulser. High-resolution (sub-ns in time and 2–3 μm in space) x-ray radiographs of X pinches driven by current pulses that rise to 200–250 kA peak current in 40 ns show that ≤300 μm long Z pinches form in the region of the original wire cross-point a few ns prior to the first sub-ns intense x-ray bursts that are characteristic of an X pinch. The Z pinches implode to ≤10 μm diam and then appear to develop gaps in the radiographic images in one or two places, coincident in time with the x-ray burst(s). The emission spectra of the intense x-ray bursts from different wire materials indicate electron temperatures of 500–1300 eV and densities in excess of 1022/cm3. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351553
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  • 8
    Electronic Resource
    Electronic Resource
    Density measurements in exploding wire-initiated plasmas using tungsten wires (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4272-4283 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calibrated density measurements have been obtained of the coronal plasmas around exploding 7.5–40 μm W wires carrying 15–120 kA per wire for 30–70 ns. X-ray radiographs of the exploding wire plasmas using 2.5–10 keV photons from a Mo wire X-pinch backlighter enabled measurements of areal densities of W ranging from 2×1017/cm2, equivalent to 0.03 μm of solid density W, to about 1019/cm2. The rapidly expanding (few mm/μs) coronal plasmas surrounding the slowly expanding (〈1 mm/μs) residual wire cores have areal densities up to about 2×1018/cm2. Single 7.5 μm wires tested with 100 kA had as much as 90% of the initial wire material in the coronal plasma. Coronal plasma W number densities were estimated to be up to a few times 1018/cm3, while core W densities as low as a few times 1020/cm3 were observed. With linear arrays of four (eight) 7.5 μm wires carrying 30 kA (15 kA)/wire, up to 35% (25%) of the initial W wire material was in the plasma around and between the wires at 46–48 ns after the current started. Preheating the wires to drive off adsorbed gases and hydrocarbons increased the W mass in the coronal plasma and made it more uniform then when wires were not preheated. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873695
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  • 9
    Electronic Resource
    Electronic Resource
    High-luminosity monochromatic x-ray backlighting using an incoherent plasma source to study extremely dense plasmas (invited) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 740-744 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new diagnostic method for dense plasmas, monochromatic x-ray backlighting, is described. In this method, shadow images of a bright, dense plasma can be obtained with high spatial resolution using monochromatic radiation from a separate plasma, permitting a major reduction in the required backlighting source power. The object plasma is imaged utilizing spherically bent mica crystals as x-ray optical elements. Experimental results, namely images of test objects obtained using x-ray radiation having different photon energies, are presented. Shadow images of exploding Al wire plasmas in the 1s2–1s2p line radiation of He-like Al XII are also shown. Spatial resolution as fine as 4 μm is demonstrated. The scheme described here is useful for backlighting extended high density plasmas, and could be a less costly alternative to using x-ray lasers for such purposes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147689
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  • 10
    Electronic Resource
    Electronic Resource
    A simple air wedge shearing interferometer for studying exploding wires : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1098-1100 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of shearing interferometer using an air wedge is described. This interferometer is based on a beam splitter constructed using two 90-degree prisms. A small air gap, which varies in spacing from top-to-bottom, separates the second prism from the first and forms the air wedge. The single incident laser beam is focused near the gap, and the two primary reflections from the long sides of each prism form the two coherent virtual sources necessary for interferometry. The shift between the two images of the object at the detector, as well as the orientation and frequency of the fringes, can be independently adjusted by altering the air gap thickness and angle, as well as the position of the laser focus in the gap. This interferometry scheme is inexpensive and easily aligned, and has been successfully and reliably used in exploding wire experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321746
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