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  • 1
    Electronic Resource
    Electronic Resource
    Generation of high-energy x-radiation using a plasma flow switch (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1999-2007 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high-voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x-radiation pulse occurs substantially after the high-voltage pulse suggesting that high-energy electrons are generated by dynamic processes in a very high speed ((approximately-greater-than)106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low-density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force-u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30-keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348773
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  • 2
    Electronic Resource
    Electronic Resource
    A master-oscillator-driven phase-locked vircator array (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3073-3079 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phase locking of a vircator array driven by a relativistic magnetron in a pure master–slave configuration has been achieved. A single high voltage pulse drives the relativistic magnetron and the vircator array in series. Phase locking occurs for ∼40 ns. The time required to lock is (approximately-equal-to)10 ns. the peak array power is (approximately-equal-to)1 GW. The injection ratio, ρ, and allowable frequency difference, Δf, relationship required for phase locking is examined. The results suggest that the Adler's inequality, ρ(approximately-greater-than)(Q/Δf) f, is a necessary, but not sufficient condition to predict phase locking. A hybrid configuration in which the driven vircators are also mutually connected together has also been attempted. Phase locking is observed with better phase stability than in the pure master–slave configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346401
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of acidic haloaluminate melts: Neutron diffraction and quantum chemical calculations (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2733-2741 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of molten mixtures of (KX)y(AlX3)1−y was investigated by neutron diffraction for X=Cl and Br and y=0.25 and 0.33. These melts, known as acidic haloaluminates, contain different ionic species such as AlX−4,Al2X−7, Al3X−10. The diffraction patterns were similar, although not identical, for the same halide pairs and showed features indicative of short-range and intermediate-range order. Quantum chemical calculations were carried out on AlX−4, Al2X−7, and Al3X−10 to provide information needed to interpret the structural results within the framework of the random packing of structural units model. It is shown that the bent Al–X–Al bridge for Al2X−7, obtained from the quantum chemical calculations, is necessary to represent well the structure, and that the values of the bond angles at the central halide atoms are around 110°. Aluminum atoms are found to be tetrahedrally coordinated by the halide atoms, and information on the orientational correlations of neighboring Al2X−7 is derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463063
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  • 4
    Electronic Resource
    Electronic Resource
    High-resolution x-ray spectrometer based on spherically bent crystals for investigations of femtosecond laser plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 4049-4053 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrashort-pulse, laser-produced plasmas have become very interesting laboratory sources to study spectroscopically due to their very high densities and temperatures, and the high laser-induced electromagnetic fields present. Typically, these plasmas are of very small volume and very low emissivity. Thus, studying these near point source plasmas requires advanced experimental techniques. We present a new spectrometer design called the focusing spectrometer with spatial resolution (FSSR-2D) based on a spherically bent crystal which provides simultaneous high spectral (λ/Δλ(approximate)104) and spatial resolution ((approximate)10 μm) as well as high luminosity (high collection efficiency). We described in detail the FSSR-2D case in which a small, near point source plasma is investigated. An estimate for the spectral and spatial resolution for the spectrometer is outlined based on geometric considerations. Using the FSSR-2D instrument, experimental data measured from both a 100 fs and a nanosecond pulse laser-produced plasma are presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149249
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  • 5
    Electronic Resource
    Electronic Resource
    Application of new synchrotron powder diffraction techniques to anomalous scattering from glasses : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1308-1310 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have applied two synchrotron powder diffraction techniques to the measurement of high quality anomalous scattering diffraction data for amorphous materials. One of these methods, which uses a curved perfect crystal analyzer to simultaneously diffract multiple powder lines into a position sensitive detector has been shown to possess high resolution, low background, and very high counting rates. This data measurement technique provides excellent energy resolution while minimizing systematic errors resulting from detector nonlinearity. Anomalous scattering data for a Cesium Germanate glass collected using this technique will be presented. The second powder diffraction technique uses a flat analyzer crystal to deflect multiple diffraction lines out of the equatorial plane. Calculations show that this method possesses sufficient energy resolution for anomalous scattering experiments when a perfect crystal analyzer is used and is experimentally much simpler. Future studies will make use of a rapid sample changer allowing the scattering from the sample and a standard material (a material not containing the anomalous scatterer) to be measured alternately at each angle, reducing systematic errors due to beam instability or sample misalignment. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145960
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  • 6
    Electronic Resource
    Electronic Resource
    Charge and mass resolved time of flight observations of 140 fs laser produced ions : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 333-335 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ions from this plasma are self-extracting with energies of 0.1 to 100 keV, the extraction potential being one of the desired observables. The charge/mass (z/μ, μ is mass in AMU) separation is provided by a static magnetic field (B⋅L=1280 G cm, FWHM=14 mm) located 5 cm from the linear (1−d) detector. Displacement along the detector axis is thus proportional to z/μ(1/v). The detector is a gold cathode MCP with a fast (sub-ns) phosphor. The phosphor output is coupled into a streak camera (typical sweep 8.5 or 24 μs total) through a coherent fiber bundle. Streak images are grabbed with a 14-bit CCD. The signature of any specific ion is a straight line of slope proportional to z/μ. Since there are usually more than one charge state of a given ion, integer multiple slopes appear. Thus z and m can be found. Absolute calibration is taken from the slope of the proton streak, which is always present with our plasmas. While providing the same information as a Thomson parabola, the straight line images are easier to extract information from and offer resolution with less energy dependence. By providing mass and time of flight information, the product of z⋅Te can be determined unambiguously during the hydrodynamic acceleration of the plasma. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146404
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  • 7
    Electronic Resource
    Electronic Resource
    Pattern of interspecific tiller defoliation in a mixed-grass prairie grazed by cattle (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 45 (1990), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Permanently marked tillers of five perennial grasses, native to the mixed-grass prairie of North America, were monitored to determine patterns of defoliation, architectural attributes influencing probabilities of defoliation. and post-defoliation responses. Frequency of tiller defoliation was greatest for one of the dominant midgrasses, intermediate for the remaining midgrass and two dominant shortgrasses. and least for the subdominant midgrass. Midgrass species, including the infrequently grazed subordinate species, were consistently grazed more intensively than the shortgrass species. However, the relative intensity of defoliation did not vary among species or grazing periods indicating that intensity of defoliation was primarily a function of pre-defoliation tiller height. Tiller architecture, including height, lamina number and the presence of reproductive culms, did not significantly influence frequency or intensity of defoliation within a species. The lack of evidence supporting tiller architecture as a selection criterion within a species suggests that animals were selecting on vegetation parameters at higher levels of vegetation organization than individual tillers. Grazed tillers of the three midgrasses exhibited greater relative rates of tiller elongation between grazing periods than non-grazed tillers, particularly early in the season when environmental conditions for growth were most favourable. The patterns of interspecific tiller defoliation observed in this study parallel the long-term patterns of grazing-induced species replacement observed in this grassland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1990.tb02201.x
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  • 8
    Electronic Resource
    Electronic Resource
    Piezoelectric copolymer hydrophones for ultrasonic field characterization (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 203-207 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Hydrophones to be used in the characterization of medical ultrasonic transducers have been fabricated using a new polyvinylidene fluoride/trifluoroethylene (VF2/VF3) copolymer. The copolymer has an advantage over VF2 in that it does not require prestretching before poling. Thin copolymer films can be cast from solution and then poled using the corona discharge method. As there is a need for small-diameter hydrophones to provide good spatial resolution in measuring highly focused ultrasonic beams, hydrophones with diameter as small as 0.1 mm have been made. Both needle-type and line hydrophones have been tested and their performance reported. In the case of line hydrophones, the output signal is proportional to the line integral of the acoustic pressure and a computer tomographic technique has been used to reconstruct the beam profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142306
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  • 9
    Electronic Resource
    Electronic Resource
    Levitation apparatus for structural studies of high temperature liquids using synchrotron radiation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3512-3518 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new levitation apparatus coupled to a synchrotron-derived x-ray source has been developed to study the structure of liquids at temperatures up to 3000 K. The levitation apparatus employs conical nozzle levitation using aerodynamic forces to stably position solid and liquid specimens at high temperatures. A 270 W CO2 laser was used to heat the specimens to desired temperatures. Two optical pyrometers were used to record the specimen temperature, heating curves, and cooling curves. Three video cameras and a video recorder were employed to obtain and record specimen views in all three dimensions. The levitation assembly was supported on a three-axis translation stage to facilitate precise positioning of the specimen in the synchrotron radiation beam. The levitation system was enclosed in a vacuum chamber with Be windows, connections for vacuum and gas flow, ports for pyrometry, video, and pressure measurements. The vacuum system included automatic pressure control and multi-channel gas flow control. A phosphor screen coupled to a high-resolution video microscope provided images of the x-ray beam and specimen shadow which were used to establish the specimen position. The levitation apparatus was integrated with x-ray diffractometers located at X-6B and X-25 beamlines at the National Synchrotron Light Source. X-ray structural measurements have been obtained on a number of materials including Al2O 3, Ni, Si, Ge, and other metallic and ceramic materials in the liquid state. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148315
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  • 10
    Electronic Resource
    Electronic Resource
    Compact toroid formation, compression, and acceleration (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2938-2958 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Research on forming, compressing, and accelerating milligram-range compact toroids using a meter diameter, two-stage, puffed gas, magnetic field embedded coaxial plasma gun is described. The compact toroids that are studied are similar to spheromaks, but they are threaded by an inner conductor. This research effort, named marauder (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation), is not a magnetic confinement fusion program like most spheromak efforts. Rather, the ultimate goal of the present program is to compress toroids to high mass density and magnetic field intensity, and to accelerate the toroids to high speed. There are a variety of applications for compressed, accelerated toroids including fast opening switches, x-radiation production, radio frequency (rf) compression, as well as charge-neutral ion beam and inertial confinement fusion studies. Experiments performed to date to form and accelerate toroids have been diagnosed with magnetic probe arrays, laser interferometry, time and space resolved optical spectroscopy, and fast photography. Parts of the experiment have been designed by, and experimental results are interpreted with, the help of two-dimensional (2-D), time-dependent magnetohydrodynamic (MHD) numerical simulations. When not driven by a second discharge, the toroids relax to a Woltjer–Taylor equilibrium state that compares favorably to the results of 2-D equilibrium calculations and to 2-D time-dependent MHD simulations. Current, voltage, and magnetic probe data from toroids that are driven by an acceleration discharge are compared to 2-D MHD and to circuit solver/slug model predictions. Results suggest that compact toroids are formed in 7–15 μsec, and can be accelerated intact with material species the same as injected gas species and entrained mass ≥1/2 the injected mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860681
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