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  • American Institute of Physics (AIP)  (1,634)
  • Wiley-Blackwell  (901)
  • 1990-1994  (2,535)
  • 1980-1984
  • 1955-1959
  • 1993  (2,535)
Collection
Keywords
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  • 1990-1994  (2,535)
  • 1980-1984
  • 1955-1959
Year
  • 1
    Electronic Resource
    Electronic Resource
    Microscopy in solid state science (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 24 (1993), S. 299-315 
    Details
    ISSN: 1059-910X
    Keywords: STEM ; PEELS ; HAADFI ; Nanolithography ; Super-resolution ; STM ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The Microstructural Physics group at the Cavendish Laboratory is actively involved in a considerable number of research projects which cover a broad range of materials science. In this paper, we describe briefly several such projects, with particular emphasis given to the application of parallel-detection electron energy loss spectroscopy (PEELS) on a scanning transmission electron microscope (STEM) to the analysis of materials such as stainless steels, catalysts, and high temperature superconductors. In addition, we describe a number of related projects that are currently being carried out in the group, particularly those which utilise and develop novel STEM imaging and analytical techniques. © 1993 Wiley-Liss, Inc.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1070240404
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  • 2
    Electronic Resource
    Electronic Resource
    Helium, iron, and electron particle transport and energy transport studies on the Tokamak Fusion Test Reactor (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2215-2228 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from helium, iron, and electron transport studies on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 26, 11 (1984)] in L-mode and supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the supershot. The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the supershot, differences are found in the L mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of 3 larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860755
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  • 3
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequency heating on the Tokamak Fusion Test Reactorf| (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2437-2444 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complete ion cyclotron range of frequency (ICRF) heating system for the Tokamak Fusion Test Reactor (TFTR) [Fusion Tech. 21, 1324 (1992)], consisting of four antennas and six generators designed to deliver 12.5 MW to the TFTR plasma, has now been installed. Recently a series of experiments has been conducted to explore the effect of ICRF heating on the performance of low recycling, supershot plasmas in minority and nonresonant electron heating regimes. The addition of up to 7.4 MW of ICRF power to full size (R∼2.6 m, a∼0.95 m), helium-3 minority, deuterium supershots heated with up to 30 MW of deuterium neutral-beam injection has resulted in a significant increase in core electron temperature (ΔTe=3–4 keV). Simulations of equivalent deuterium–tritium (D–T) supershots predict that such ICRF heating should result in an increase in βα(0)∼30%. Direct electron heating has been observed and has been found to be in agreement with theory. The ICRF heating has also been coupled to neutral-beam heated plasmas fueled by frozen deuterium pellets. In addition ICRF heated energetic ion tails have been used to simulate fusion alpha particles in high-recycling plasmas. Up to 11.4 MW of ICRF heating has been coupled into a hydrogen minority, high-recycling helium plasma and the first observation of the toroidal Alfvén eigenmode (TAE) instability driven by the energetic proton tail has been made in this regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860728
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  • 4
    Electronic Resource
    Electronic Resource
    Improvement of FMR linewidth in Bi-substituted lutetium iron garnet thin films for the MSW-optical-mode interaction : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6460-6462 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of bismuth-substituted lutetium iron garnet (BiLuIG) for the magnetostatic wave (MSW)-optical-mode interaction can be grown by liquid-phase epitaxy from the standard PbO-based melt system developed for yttrium iron garnet (YIG). The addition of MgO to the melt to counteract the effect of lea on the ferromagnetic resonance (FMR) linewidth is investigated. BiLuIG thin films were grown on paramagnetic gadolinium gallium garnet substrates with varying amounts of MgO added. The ferromagnetic resonance linewidth, optical waveguide absorption, and MSW passband were measured. The addition of magnesium reduced the FMR linewidth from an average of 3 Oe down to under 1 Oe, with little effect on other parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352579
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  • 5
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of the N3 radical (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2616-2631 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation dynamics of the B˜ 2Σu+ state of N3 were investigated using fast radical beam photodissociation coupled with a new coincidence wedge-and-strip-anode particle detector. With this detector, detailed photofragment kinetic energy and angular distributions can be measured as a function of excitation energy. Calibration of the detector by studies of the predissociation of the O2 B 3Σu− state is discussed. Methods of extracting the center-of-mass kinetic energy and angular distributions are presented. The photodissociation results for N3 show that from the vibrationless level of the B˜ 2Σu+ state in N3, both spin-allowed [N3→N(2D)+N2(1Σg+)] and spin-forbidden [N3→N(4S)+N2(1Σg+)] dissociation processes occur. Bend excitation in the B˜ 2Σu+ state, however, enhances the spin-allowed dissociation process considerably. The kinetic energy distributions reveal partially resolved vibrational structure in the N2 fragment, and indicate substantial rotational excitation of the N2. This implies that bent geometries play a major role in the dissociation of the N3 B˜ state. Possible mechanisms for the spin-forbidden and spin-allowed dissociation channels are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465224
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  • 6
    Electronic Resource
    Electronic Resource
    Fast beam photodissociation of the CH2NO2 radical (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8751-8764 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of the nitromethyl radical, CH2NO2, has been studied using a fast beam photofragment translational spectrometer. In these experiments, a fast beam of mass selected, internally cold nitromethyl radicals is formed via negative ion photodetachment of CH2NO−2 and subsequently dissociated. The recoiling photofragments are detected in coincidence using a microchannel plate detector equipped with a time- and position-sensing anode. Two dissociation product channels are observed at each of three dissociation wavelengths investigated in the range 240–270 nm and are identified as (I) CH2NO2→CH2NO+O and (II) CH2NO2→H2CO+NO. In marked contrast to the ultraviolet photodissociation of CH3NO2, no evidence is found for simple C–N bond fission to give (III) CH2NO2→CH2+NO2. Translational energy and angular distributions were obtained for the two observed channels. The translational energy distribution of channel (I) peaks at only 5–8 kcal/mol, while the distribution for channel (II) peaks at ∼60 kcal/mol. The angular distributions for both channels are largely isotropic. The nature of the electronic excitation and dissociation dynamics are considered at length. The upper state in the electronic transition is assigned to the 1 2B1 state. Results of attempts to model various aspects of the dissociation dynamics as statistical processes on the ground state surface indicate this mechanism is very unlikely. Instead, both dissociation channels are believed to occur primarily on excited state surfaces, and mechanisms for these processes are proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465597
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A comparison of edge turbulence in tokamaks, stellarators, and reversed-field pinches* (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2491-2497 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Edge equilibrium, turbulence and transport related plasma parameters from the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] torsatron, the ZT-40M [Fusion Technol. 8, 1571 (1985)] reversed-field pinch, the Phaedrus-T [Nucl. Fusion 32, 2040 (1992)] tokamak, the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)], and the Tokamak Fusion Test Reactor (TFTR) [in Plasma Physics and Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] have been obtained using a standardized Langmuir probe array and a consistent set of data analysis packages. Additional data from some other devices have also been furnished via private communications and incorporated from published results. Experimental results over a wide range of parameters are compared and the turbulence contribution to edge transport are assessed. Certain physical properties that are relevant to the modeling of edge turbulence are identified: namely, shear decorrelation of turbulence, the role of resistive dissipation and electron parallel thermal conduction, radial mode structure in sheared magnetic field, and electromagnetic contribution to the parallel Ohm's law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860734
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  • 9
    Electronic Resource
    Electronic Resource
    Suppression of m=2 islands by electron cyclotron heating in the Texas Experimental Tokamak: Experiment and theory (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3239-3245 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron cyclotron heating (ECH) is used to suppress m=2 magnetohydrodynamic (MHD) oscillations in the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)]. The location of ECH power deposition is controlled by a movable antenna. The MHD activity is suppressed when the ECH beam is directed close to the q=2 surface. The experiment is simulated using a three-dimensional resistive MHD code in cylindrical geometry. For fixed plasma current, the saturated m=2 island width is found to depend on the value of the safety factor at the magnetic axis (q0). The simulation suggests that the observed saturated m=2 island in the pre-ECH plasma, which typically occupies 25% of the minor radius, corresponds to q0∼1.3. The suppression of the island in the presence of ECH is attributed to current profile modification. In some discharges, the m=2 activity does not resume even after the ECH pulse is turned off.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860659
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  • 10
    Electronic Resource
    Electronic Resource
    Intense ion-beam-transport experiments using a z-discharge plasma channel (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 176-189 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A z-discharge plasma channel is used to confine and transport an intense proton beam. A pinch-reflex ion diode on the NRL Gamble II accelerator focuses a proton beam onto the entrance aperture of a 2.5 cm diam, 1.2 m long z-discharge transport system. The beam ions are charge and current neutralized in the discharge plasma, and execute betatronlike orbits in the magnetic field of the discharge. Ion beam diagnostics include shadowbox imaging and prompt-γ radiation measurements from LiF targets. Under appropriate conditions, 95% particle transport and 90% energy transport are observed, with the only energy loss attributed to classical stopping in the channel gas. The transverse phase-space distribution of the beam measured by the shadowbox is consistent with full charge and current neutralization of the transported beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860851
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