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  • 21
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 5108-5117 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recently developed high pulse rate intense ion beam diode has been exploited to measure the relative density profile of electrons in the ion diode's acceleration gap as a function of time. This diode was magnetically insulated and it produced 100 keV Ar+ beams at up to 4 A/cm2 using an active anode plasma ion source. The diode also had a backfill of 10−2 Torr of He that was collisionally excited by energetic electrons in the acceleration gap. When the excited He atoms radiatively decayed, the emitted light was measured and used to deduce the relative electron density profile with space and time resolution. The profile was peaked toward the center of the gap and dropped off significantly toward both the anode and the cathode. The absence of electron density near the physical cathode is evidence for magnetic field profile modification from the diamagnetic drift of the electrons in the diode. With a macroscopic electric field of order 100 kV/cm, the electron current takes many tens of nanoseconds, from the moment the cathode begins to emit, to reach the Child–Langmuir current. The extent to which this limit is exceeded depends strongly on the profile of the insulating magnetic field and appears to be dominated by the dynamics of the electron flow in the diode gap. In contrast, the delay between when electrons are first observed in the gap spectroscopically and when the ion beam is first formed is independent of the magnetic field profile. This delay is about the time that it takes an argon ion to transit the acceleration gap, suggesting that ion inertia is the rate limiting factor. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 22
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1872-1876 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An active anode plasma source has been developed for use in a magnetically insulated ion diode operated on a 1010-W pulsed power generator. This source uses an inductive voltage from a single turn coil to beak down an annular gas puff produced by a supersonic nozzle. The resulting plasma is magnetically driven toward the radial insulating magnetic field in the diode accelerating gap and stagnates at a well-defined surface after about 300 ns to form a plasma anode layer defined by magnetic flux surfaces. An ion beam is then extracted from this plasma layer by applying a 150-kV, 1-μs pulse to the accelerating gap. Optimization of the timing of the gas puff, the plasma production discharge, and the high voltage pulse has resulted in 1-μs duration 75–150-keV ion beam pulses with 〉100-A/cm2 peak ion current density over an area of about 400 cm2. Up to 5 J/cm2 has been collected by a 4-cm2 calorimeter. The diode impedance history can be varied so that rising, flat, and falling voltage pulse waveforms can be produced. Streak photographs of beamlets impinging on a scintillator and time integrated targets both show beam divergence angles ≤3°. However, under certain operating conditions, large excursions (∼25°) in mean aiming angle on time scales of 20–200 ns are observed.
    Type of Medium: Electronic Resource
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  • 23
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4095-4101 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preionized plasma has been compared with vacuum and with neutral gas as a medium for the propagation of intense ion beams across magnetic fields. Two cusp-injection ion ring experiments have been used to study the effectiveness of these three cusp-fill media for space-charge neutralization, as shown by the subsequent spreading of the injected rings. In the ion ring experiment a (approximately-less-than)100-ns ion beam was injected into ∼20-eV plasma fills of (approximately-less-than)1012/cm3, giving much better propagation than vacuum, but not as good as 100-mTorr H2 gas. In the long-pulse ion ring experiment with (approximately-greater-than)200-ns beam rise time, plasma fill and vacuum gave similar propagation. The results suggest that for complete neutralization of space charge in ion beams propagating across magnetic fields, background media must be provided to meet certain minimum requirements of conductivity and collisionality which depend upon the beam current and rise time.
    Type of Medium: Electronic Resource
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  • 24
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4781-4785 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the distributions of ion transverse velocities in the acceleration gap of a magnetically insulated ion diode. The measurement is based on observing the spectral profile of the Doppler-broadened spontaneous line emission from accelerating ions. The velocity distributions of C++ and Al++ ions were peaked at zero transverse velocity and symmetric with respect to the directions parallel and antiparallel to the magnetic-field lines. The mean transverse velocities for both of the ion species corresponded to energies of about 200 eV in experiments with a gap potential difference of 260–330 kV. The divergence angles observed for both of the ion species are significantly smaller than previously observed for protons outside the diode.
    Type of Medium: Electronic Resource
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  • 25
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1655-1670 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A parametric study of microwave radiation emitted from an "applied Bθ'' magnetically insulated ion diode, covering frequencies between 0.3 and 85 GHz, indicates that collective mechanisms are responsible for the 1–10-MW peak output. These collective mechanisms may also be related to the degradation in ion beam quality seen by a scintillator/streak camera diagnostic. This degradation is most apparent when the microwave flux is at its maximum. A deformation of the plasma appears to be the most likely cause of the disturbances seen in the ion beam.
    Type of Medium: Electronic Resource
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  • 26
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Plasma formation from exploding individual wires and multiwire arrays, powered by a 450 kA, 100 ns pulsed power generator has been studied with x-ray direct backlighting using one or more X pinches as a source of radiation. Experiments have been carried out with many different wire materials ranging in Z from Al to Au. A point source of x rays is used to cast a shadow image of the object plasma directly on film ("point-projection" backlighting). Spatial resolution in the range 1–5 μm, and temporal resolution of 0.7–2 ns, has been achieved using 2–4 keV x rays from Mo wire X pinches. Different schemes for multiframe imaging are described. We also present observations of micron scale structure on residual dense wire cores 40–70 ns after the start of the current pulse. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 27
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 589 (1990), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 28
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3069-3087 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of an ion ring in a 2.5 m long, 0.30 m diam magnetized plasma column was studied using an axial array of magnetic probes and fast proton detectors, a microwave interferometer, and a grating spectrometer. The ring propagated with an initial axial velocity 3×106 m/sec, about four times the Alfvén speed in the plasma, and excited damped magnetosonic waves whose peak amplitude depended on the plasma return current. The plasma electrons were heated by about 1 eV in response to the ring, as measured by the Hγ line-to-continuum intensity ratio. This heating is primarily attributed to classical Coulomb collisions, although about 1%–10% can be attributed to the collective ring–plasma interaction. The collective interaction had no measurable effect on the dynamics of the ion ring, consistent with theoretical models, given the beam, plasma, and magnetic-field parameters in the experiment.
    Type of Medium: Electronic Resource
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  • 29
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2815-2815 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The X pinch, in which two or more crossed wires are stretched between the electrodes of the 0.5 TW LION accelerator, is being studied as a bright x-ray source for photopumping an extreme ultraviolet (XUV) laser and for microlithography. Crossed Al or Mg wires with line density from 10 to 400 μg/cm have been imploded by up to 550 kA current for 40 ns. High density and temperature bright spots have been observed at the crossing point. Diagnostics include x-ray pinhole cameras, streak and framing cameras, and XUV x-ray spectrographs. The visible streak camera provides time and radial (or axial) spatially resolved information on the pinch plasma, while the 5 ns single frame camera gives spatially resolved images. The size of the soft x-ray hot spots (less than 40 μm diameter) was estimated from the time-integrated pinhole image. An x-ray spectrograph with a curved mica crystal was used to record K-shell emission spectra. From the line intensity ratios of the K-shell radiation, plasma densities of ∼1020 cm−3 and temperatures about 400 eV were obtained. This work was supported in part by the Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5000, under ONR contract N00014-90-J-2002 and NSF grant 89-19960.
    Type of Medium: Electronic Resource
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  • 30
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 26 (1996), S. 651-691 
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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