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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2162-2164 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Previous time- and space-resolved x-ray measurements on a small gas-puff Z pinch indicated the presence of bursts of energetic electron beam and related "hot spots''—high-temperature, high-density plasma regions. Spectra taken from these hot spots are consistent with a plasma of electron density about 1022–1023 cm−3 and electron temperature of 500 eV. Here we present time correlation of the hard x-ray emission from the anode with large fluctuations in I(overdot) and with short bursts of intense soft x rays. These soft x-ray bursts originating from the hot spots are shown always to be preceded by hard x-ray emissions. Using suitable apertures, the plasma is shown to be a source of hard x rays, 〈2.5 A(ring). This is confirmed by x-ray pinhole photographs. By varying the Z of the anode the electron beam associated with hard x-ray emission is found to be of low energy (10 keV) agreeing with previous measurements. In particular a plastic, PTFE (Teflon), is shown to be a suitable material for the anode, with superior lifetime performance compared with conventional metallic substances.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3385-3390 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: XUV and x-ray emission spectra of the elements carbon, oxygen, neon, and argon, in the spectral range 3–300 A(ring), generated in a gas-puff z pinch, are presented. The spectra are analyzed to give time-integrated measurements of the density, electron temperature, and dimensions of the imploded plasma and the "hot spots'' that often occur in the gas-puff pinch. In particular, dielectronic satellite lines are used to measure the electron density and temperature, and Stark broadening to measure electron density. The effect of optical depth is included.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1672-1680 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Z pinch is enjoying a renaissance as the world's most powerful yet efficient soft x-ray source which can energize large volume hohlraums for indirectly driven inertial confinement fusion. It has the advantages of being efficient and having high energy and power density. Its early history will be traced from the 18th century to the present day. The most notable feature of the Z pinch is its instability. The various regimes of stability analysis will be reviewed, including resistive and finite ion Larmor radius effects. Work in the last 10 years on single fibres, especially of cryogenic deuterium, gave neutrons that were of the same origin, namely, beam–plasma interactions, as reported by Kurchatov. The renaissance has come about through the implosion of arrays of fine wires. Research at Sandia National Laboratory has shown that by using more and finer wires, the x-ray radiation emitted at stagnation increased in power and decreased in pulse width. The understanding of these results has been advanced considerably by theory, simulation and smaller-scale, well diagnosed experiments showing the early uncorrelated m=0 instabilities on each wire, the inward jetting of plasma to the axis, the global Rayleigh–Taylor instability and the mitigating effect of nested arrays. © 2000 American Institute of Physics.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 1019 W cm-2 at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and γ-rays. ...
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid ...
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Huge magnetic fields are predicted to exist in the high-density region of plasmas produced during intense laser–matter interaction, near the critical-density surface where most laser absorption occurs, but until now these fields have never been measured. By using pulses focused to extreme ...
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  • 7
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 682-691 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2579-2587 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments on Z-pinch plasmas, driven by a pulsed power generator that delivers 160 kA with a rise time (10%–90%) of 65 ns are reported. Tungsten wires of various diameters were used and results are compared with 15 μm diameter aluminum wire. The expansion of the pinch is studied as a function of wire diameter and material. Schlieren observations show that the coronal plasma of various diameters of tungsten wires expands with the velocity of (9.4±1.0)×103 m/s. The aluminum pinch expands at least a factor of 2 faster. The m=0 perturbations appear at about 8 ns for the aluminum compared with 20 ns for the tungsten pinch. The wavelength and diameter of the perturbations increase with time for both types of wires, and relatively faster for the aluminum pinch. The short wavelength perturbations (∼200 μm) persist for a longer time for larger diameter tungsten wires. Bright spots are seen to appear after 60 ns from the current start for tungsten wires, whereas for aluminum wires, bright spots appear after 40 ns. The decay time of bright spots is 40 ns for the smallest diameter tungsten wire compared with only a few nanoseconds for larger diameter wires. Hard x-ray emission above 6 keV was observed from tungsten wire pinches, but it was not observed from either bright spots or the plasma column for the aluminum pinch. However, hard x-ray emission from the anode due to an electron beam was observed for wires of both materials. © 1999 American Institute of Physics.
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