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  • 2000-2004  (13)
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Materialart
Erscheinungszeitraum
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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1458587
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1323759
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873825
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873975
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1351553
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  • 6
    Digitale Medien
    Digitale Medien
    Laser-driven atomic-probe-beam diagnostics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4409-4414 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new laser-driven atomic-probe-beam diagnostic (LAD) is proposed for local, time-resolved measurements of electric field and ion dynamics in the accelerating gap of intense ion beam diodes. LAD adds new features to previous Stark-shift diagnostics which have been progressively developed in several laboratories, from passive observation of Stark effect on ion species or fast (charge-exchanged) neutrals present naturally in diodes, to active Stark atomic spectroscopy (ASAS) in which selected probe atoms were injected into the gap and excited to suitable states by resonant laser radiation. The LAD scheme is a further enhancement of ASAS in which the probe atoms are also used as a local (laser-ionized) ion source at an instant of time. Analysis of the ion energy and angular distribution after leaving the gap enables measurement, at the chosen ionization location in the gap, of both electrostatic potential and the development of ion divergence. Calculations show that all of these quantities can be measured with sub-mm and ns resolution. Using lithium or sodium probe atoms, fields from 0.1 to 10 MV/cm can be measured. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1324738
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1321746
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  • 8
    Digitale Medien
    Digitale Medien
    Point-projection x-ray radiography using an X pinch as the radiation source : 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. 667-670 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Using an X pinch as a source of radiation for point-projection radiography, it is possible to project a high-resolution (1–10 μm) shadow image of dense plasma or test objects onto x-ray-sensitive film. The emission characteristics of X pinches composed of a wide variety of materials have been studied using several diagnostics. The pulse duration and shape of the x-ray bursts were measured in the 1.5–6 keV band using fast diamond PCDs and an x-ray streak camera with sweep speeds as fast as 10 ns for the full sweep (3.5 cm). To investigate the line and continuum radiation emitted by the X pinches, a convex spectrograph using a mica or KAP crystal, and a spectrograph based on a spherically bent mica crystal were used. Summarizing the data, including radiography results, wires known to have slower expansion rates and high boiling temperatures (NiCr, Ti, Nb, Mo, Pd, Ta, W, and Pt) appeared to yield the smallest x-ray source sizes, i.e., gave the best spatial resolution in radiographs and provided subnanosecond time resolution. All of these materials yield intense continuum radiation with energy up to 6 keV, and the highest resolution images are achieved using only the continuum radiation from the X pinch. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1323252
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  • 9
    Digitale Medien
    Digitale Medien
    Temporal parameters of the X-pinch x-ray source (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2948-2956 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The X pinch has proved to be an excellent source of 2.5–10 keV radiation for point-projection radiography with spatial resolution of 2 μm or even better. The pulse duration of the x-ray bursts has been investigated for a wide variety of wire materials in the 1.5–10 keV energy range using a set of fast diamond photoconducting detectors with different filters, and using an x-ray streak camera to observe the source through four different filters on each pulse. All wires tested have intense continuum up to at least 6 keV, and the duration of the pulse is shorter for the harder radiation component for all materials. However, there are substantial differences between materials. For example, the pulse duration for Al with filtering for energy ≥1.5 and ≥5 keV are about 1 and 0.5 ns, respectively. By contrast, for Mo with filtering for energy ≥2.5 and ≥5 keV, the pulse durations are about 200 ps and ≤80 ps, respectively. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1379961
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  • 10
    Digitale Medien
    Digitale Medien
    Telescopic refractive index gradient diagnostic of an ion diode anode plasma (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2310-2321 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We present a general analysis of possible variants of refractive index gradient (RING) diagnostics with a laser beam probe. Using a differential bicell photodiode as a detector, the sensitivity, dynamic range, and geometric restrictions of RING deflectometry have been found for lensless, one lens, and "three-telescope" optical schemes. The three-telescope method is found to be the most flexible and easily aligned. If the refracted/deflected laser beam cross section in the back focal plane of the output lens is also recorded using a fast framing camera, measurements of the beam deflection and its spatial frequency spectrum after passing through the refractive medium can be obtained simultaneously. A general relation is presented between the Fourier transform of a Gaussian beam by the output lens and the spatial frequency spectrum of the inhomogeneities. From these considerations, we present the specific design of a RING diagnostic for study of anode plasma evolution in a magnetically insulated ion diode on the Cornell Beam Research Accelerator (COBRA) (800 kV, 80 ns pulse). The maximum density gradient was found to be located about 0.4 mm from the anode surface at the peak of the diode voltage pulse. The electron density at this position was about 2×1015 cm−3. The transverse spatial frequency distribution of the probe laser beam after passing through the anode plasma was recorded using the optical Fourier transform technique. This experiment demonstrates that the combined integrated deflection. (RING) and Fourier transform optical techniques can give a great deal of information about this thin (∼1 mm) anode plasma layer. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1362457
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