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  • 1
    Electronic Resource
    Electronic Resource
    Measurements of the trapped particle sideband instability compared to the macroparticle model (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3457-3466 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The upper and lower sidebands are measured on a traveling wave tube where a cold electron beam is trapped by a large amplitude wave. The two strongly coupled sidebands form a normal mode that is characterized by the sideband growth rates, wave number shifts, amplitude ratio, and phase relationship. The measured values agree only qualitatively with the macroparticle model of Kruer, Dawson, and Sudan [Phys. Rev. Lett. 23, 838 (1969)]. Also, the macroparticle model prediction for a nonlinear product wave does not agree with the experiment. Quantitative agreement is found between the experiment and computer simulations that follow the electron orbits, suggesting that the trapped particle model is too simple for quantitative predictions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1379341
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  • 2
    Electronic Resource
    Electronic Resource
    Confinement and manipulation of non-neutral plasmas using rotating wall electric fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2776-2789 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A "rotating wall" perturbation technique enables confinement of up to 3×109 electrons or 109 ions in Penning–Malmberg traps for periods of weeks. These rotating wall electric fields transfer torque to the particles by exciting Trivelpiece–Gould plasma modes with kz≠0 and mθ=1 or 2. Modes that rotate faster than the plasma column provide a positive torque that counteracts the background drags, resulting in radial plasma compression or steady-state confinement in near-thermal equilibrium states. Conversely, modes that rotate slower than the plasma provide a negative torque, and enhanced plasma expansion is observed. The observed Trivelpiece–Gould mode frequencies are well predicted by linear, infinite-length, guiding-center theory. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874128
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  • 3
    Electronic Resource
    Electronic Resource
    Measurement of cross-magnetic-field heat transport due to long-range collisions : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1767-1773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cross-magnetic-field heat transport in a quiescent pure ion plasma is found to be diffusive and to be dominated by long-range "guiding center" collisions. In these long-range collisions, which occur in plasmas with Debye length λD greater than cyclotron radius rc, particles with impact parameters rc〈ρ≤λD exchange parallel kinetic energy only. The resulting thermal diffusivity χL is independent of magnetic field B and plasma density n. The measured thermal diffusivity χ agrees within a factor of 2 with the long-range prediction χL=0.49nv¯b2λD2 over a range of 1000 in temperature, 50 in density, and 4 in magnetic field. This thermal diffusivity is observed to be up to 100 times larger than classical diffusivity from short-range velocity-scattering collisions. These long-range collisions are typically dominant in unneutralized plasmas, and may also contribute to electron heat transport in neutral plasmas. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873997
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  • 4
    Electronic Resource
    Electronic Resource
    Solubility of zinc oxide-eugenol and calcium hydroxide cements in simulated dentinal fluid (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral rehabilitation 16 (1989), S. 0 
    Details
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The solubility of four dental cement bases was measured in simulated dentinal fluid and distilled water to evaluate the relevancy of the American Dental Association solubility test for cement bases in contact with vital dentine. A simulated dentinal fluid was formulated utilizing glucose, distilled water, and sterile human plasma. Cement-base samples were immersed in either distilled water or simulated dentinal fluid at 37°C in a shaker water-bath for 1, 2, or 3 months. Weight loss values were compared utilizing a three-way analysis of variance. Zinc oxide-eugenol cements were significantly more soluble in simulated dentinal fluid than distilled water, while the calcium hydroxide cement bases were significantly more soluble in distilled water than simulated dentinal fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2842.1989.tb01365.x
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  • 5
    Electronic Resource
    Electronic Resource
    Transport and sawtooth oscillations from rotational pumping of a magnetized electron plasma (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1813-1819 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Definitive measurements have been made of cross-field transport from "rotational pumping'' of a magnetized electron column. Rotational pumping is the collisional dissipation of the axial compressions that are caused by E×B rotation of the column through asymmetric confining potentials; it is analogous to the magnetic pumping that damps poloidal rotation in tokamaks. The transport rate is measured over a wide range of plasma parameters, including four orders of magnitude in temperature. A new theory by Crooks and O'Neil shows excellent agreement with the measured rates when the three-dimensional plasma end shapes are numerically calculated using the measured charge density profiles and temperatures. When the plasma displacement is destabilized by a resistive wall and damped by rotational pumping, a complex, nonlinear evolution is observed: a quiescent period is followed by "sawtooth'' oscillations of displacement and temperature accompanied by "bursts'' of radial transport. This behavior is due to the nonmonotonic temperature dependence of the transport rate. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871684
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  • 6
    Electronic Resource
    Electronic Resource
    The finite length diocotron mode (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 601-607 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple model is presented of a finite length electron plasma column supporting a small amplitude diocotron wave with mode number m=1. The electrons are contained inside conducting cylinders in an axial magnetic field, with negative voltages on end cylinders providing axial containment. The m=1 diocotron mode is the E×B drift orbit of an offset electron column around the cylinder axis, due to radial electric fields from image charges on the wall. The model predicts that the mode frequency will be higher than that of an infinitely long column due to θ-drifts from the radial containment fields at the plasma ends. The predicted dependencies on plasma length, radius, and temperature agree well with experiments, where frequency increases up to 2.5× are observed. For very short plasmas, these containment fields predominate over the image charge fields, and the plasma orbit is called the "magnetron" mode. The shift in the magnetron frequency due to image charges is also calculated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872752
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  • 7
    Electronic Resource
    Electronic Resource
    Sawtooth oscillations in a damped/driven cryogenic electron plasma: Experiment and theory (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2062-2071 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements have been made of nonlinear sawtooth oscillations of the displacement of a magnetized electron column in a cryogenic, cylindrical trap. First reported 7 years ago, these oscillations occur when the displacement is destabilized by a resistive wall and damped by a temperature-dependent collisional viscosity. A typical evolution can last for thousands of seconds. Measurements show that oscillations of the plasma displacement are accompanied by oscillations in the plasma temperature. A simple predator-and-prey model of the temperature and displacement gives rise to a limit cycle solution due to the nonmonotonic dependence of the viscosity on temperature. These limit cycles are in good quantitative agreement with the measured sawtooth oscillations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872372
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  • 8
    Electronic Resource
    Electronic Resource
    Electron plasma profiles from a cathode with an r2 potential variation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1265-1272 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple one-dimensional model of Maxwellian injection into a cylindrical Penning–Malmberg trap is presented. This model is used to predict the radial density profile of an electron column produced by a biased cathode with an r2 potential variation. The column density n(r) is assumed to depend upon the cathode potential voltage Vk(r) and the self-consistent space-charge potential φ(r) as n(r)∝exp{e[φ(r)−Vk(r)]/T}. A one-parameter family of theoretical solutions describes the radial density profiles. The model's predictions agree well with electron density profiles resulting from a spiral tungsten filament measured over a wide range in cathode voltages. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872784
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  • 9
    Electronic Resource
    Electronic Resource
    Test particle transport from long-range collisions : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1552-1558 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Enhanced cross-magnetic-field diffusion of test particles in pure ion plasmas has been measured. The ion plasma is contained in a Penning-Malmberg trap for weeks near thermodynamic equilibrium, characterized by rigid rotation and uniform density and temperature. Plasma expansion and loss is suppressed by a "rotating wall" technique, i.e., a weak electrostatic potential rotating faster than the plasma. Test particle transport is then measured even though there is zero net transport, in a regime where neutral collisions are negligible. The observed test particle transport is diffusive, i.e., proportional to the gradient of the test particle concentration. The measured diffusion coefficients scale as nT−1/2B−2 over a range of 40 in density, 50 in temperature, and 5 in magnetic field. This diffusion is about ten times greater than predicted by classical collisional theory, which describes velocity-scattering collisions with impact parameters ρ(approximately-less-than)rc. The enhanced transport is thought to be due to non-velocity-scattering "E×B drift" collisions with rc〈ρ(approximately-less-than)λD. Initial estimates of diffusion due to these long-range collisions are three times less than the measurements, and substantial theory questions remain. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872359
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  • 10
    Electronic Resource
    Electronic Resource
    Measurements of the weak warm beam instability (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 654-677 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments are described on the interaction of a weak warm beam with a broad spectrum of unstable waves on a traveling wave tube. The wave–particle interactions are similar to those in beam–plasma systems, and are traditionally described by quasilinear theory. The precise wave evolution is obtained by launching a specified waveform, allowing it to interact with the beam, and analyzing the received waveform. Significant mode coupling is observed, resulting in saturated waves correlated less than 0.5 with their launch values. Experimentally, each wave is separated into a component proportional to the launch amplitude and a component due solely to mode coupling. The measured properties of these separate components agree quantitatively with a four-wave coupling model. Strongest coupling is observed between waves whose wave numbers match within about an inverse turbulent trapping length. In the linear growth regime, the measured ensemble-averaged wave growth rates and beam velocity diffusion rates agree reasonably with quasilinear and resonance-broadening theory; in the nonlinear regime near saturation, the discrepancies become larger. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871418
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