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  • 1
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    Argon metastable production in argon-helium microplasmas (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-06-21
    Description: Microwave resonator-driven microplasmas are a promising technology for generating the high density of rare-gas metastable states required for optically pumped rare gas laser systems. We measure the density of argon 1s 5 states (Paschen notation) in argon-helium plasmas between 100 Torr and atmospheric pressure using diode laser absorption. The metastable state density is observed to rise with helium mole fraction at lower pressures but to instead fall slightly when tested near atmospheric pressure. A 0-D model of the discharge suggests that these distinct behaviors result from the discharge being diffusion-controlled at lower pressures, but with losses occurring primarily through dissociative recombination at high pressures. In all cases, the argon metastable density falls sharply when the neutral argon gas fraction is reduced below approximately 2%.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Surface plasmon wave plates (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-01-28
    Description: Here, we investigate both numerically and experimentally, the polarization conversion capabilities of a rectangular array of holes with two unequal orthogonal periodicities. We show that it is possible to tune the periodicities in such a way that the transmitted light is circularly polarized for a nominated wavelength, λ CPL , when the structure is illuminated with appropriately oriented linearly polarized light at normal incidence. A device was fabricated and experiments confirmed that a degree of circular polarization of 0.89 could be achieved at the resonant wavelength.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Drag and torque coefficients for plate and disk induced stokes flows with slip (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-12-10
    Description: A key purpose of this paper is to demonstrate that the introduction of slip changes the structure of viscous flow past plates and disks by precluding edge singularities in the stresses. It is well-known that the inviscid limit flow is not recovered by letting the viscosity tend to zero. Here it is demonstrated that, similarly, the no-slip limit flow is not recovered by letting the slip coefficient tend to zero. For each of the three cases involving a translating plate and a rotating or translating disk, the determination of the tangential stress is reduced to a linear system of equations with simple coefficients. Values of the drag or torque and edge stresses are displayed.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
    Electronic Resource
    Electronic Resource
    Molecularly chemisorbed intermediates to oxygen adsorption on Pt(111): A molecular beam and electron energy-loss spectroscopy study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3696-3704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High translational energy adsorption of oxygen on the (111) surface of platinum was examined with electron energy loss spectroscopy (EELS) and molecular beam techniques. EEL spectra indicate that over an incident energy range of 0.2–1.37 eV and on a Pt(111) surface held at 77 K, oxygen adsorbs in an associative chemisorbed state—yielding to the dissociated state only after sufficient substrate heating. Simple direct dissociation appears negligible for all incident kinetic energies studied. At near-zero surface coverages, exclusive population of the peroxolike molecular precursor is observed for adsorption at these high translational energies, while both superoxolike and peroxolike forms are detected for low energy adsorption (0.055 eV). This peculiarity represents evidence that translational energy is effective in differentially populating reaction intermediates and provides better quantification of potential energy barriers to dissociation. We estimate the activation barrier for dissociation from the peroxolike precursor to be approximately 0.29 eV. Initial adsorption probability measurements over a wide range of surface temperatures and high incident kinetic energies corroborate a molecular chemisorption mediated mechanism. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479649
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  • 5
    Electronic Resource
    Electronic Resource
    An efficient tabulated collisional radiative equilibrium radiation transport model suitable for multidimensional hydrodynamics calculations (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3480-3489 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A computationally efficient method for transporting radiation in multidimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multidimensional radiation transport problem. This method is superior to diffusion methods because (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent nonlocal thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multidimensional calculations. Given the internal energy and ion density, and by calculating the line probability of escape from a zone of the multidimensional plasma, the equation of state, including emissivities and absorption coefficients, of the zone is determined from the table. Total radiative power, K-shell radiative power, total radiative yield, K-shell radiative yield, and plasma density and temperature profiles obtained from 1D Z-pinch calculations employing this method are in good agreement with the same powers, yields, and profiles calculated using a full radiation transport model. This method has been implemented in the 2D plasma radiating imploding source model code [F. L. Cochran et al., Phys. Plasmas 2, 2765 (1995)] to determine the influence of radiation transport in argon Z-pinch experiments performed on the Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1373415
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  • 6
    Electronic Resource
    Electronic Resource
    3He refrigerator based very low temperature scanning tunneling microscope (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1459-1463 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design and development of a scanning tunneling microscope (STM) which can operate at temperatures down to 240 mK and in magnetic fields up to 7 T with high spatial and energy resolution. The compact and rigid STM head is mounted directly on a low vibration, single shot, 3He refrigerator. This refrigerator can be operated at its base temperature continuously for several days before the 3He needs to be recondensed. The system is equipped with a sample transport manipulator from room temperature, and a cleavage device at low temperature, so that the cryogenic ultrahigh vacuum condition inside the cryostat can be utilized. A superconducting magnet provides a magnetic field of up to 7 T at the sample along the STM tip direction. Test results have shown that, at the base temperature, this instrument has better than 0.5 pm z-direction resolution in imaging mode, and better than 20 μV energy resolution in spectroscopy mode. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149605
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  • 7
    Electronic Resource
    Electronic Resource
    Synergistic methane formation kinetics for hydrogen impact on carbon (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3293-3299 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A physical/chemical model is presented for the reaction kinetics for methane formation from carbon, due to bombardment by energetic (∼100's eV) H+ ions and thermal (∼1 eV) H0 atoms. While the model was developed for H+ and H0, it can be readily applied to nonhydrogenic energetic particles (ions or atoms, e.g., Ar+, He+, He) in combination with thermal (∼1 eV) hydrogen (again ions or atoms) impacting on carbon. Both collisional (in the case of the energetic particles) and chemical reaction processes are included. Special cases of sub-eV H0 alone, energetic H+ alone, and combined H0 plus H+ were considered and fitted to experimental data. Generally good agreement was found between theoretical predictions and experimental results over the experimental flux and H+ energy ranges studied (H0 flux: 6×1014–7×1015 H0/cm2 s, H+ flux: 6×1012–5×1015 H+/cm2 s, H+ energy: 300 eV/H+ and 1 keV/H+).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450999
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  • 8
    Electronic Resource
    Electronic Resource
    Model of enhanced energy deposition in a Z-pinch plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3265-3277 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In numerous experiments, magnetic energy coupled to strongly radiating Z-pinch plasmas exceeds the thermalized kinetic energy, sometimes by a factor of 2–3. An analytical model describing this additional energy deposition based on the concept of macroscopic magnetohydrodynamic (MHD) turbulent pinch heating proposed by Rudakov and Sudan [Phys. Reports 283, 253 (1997)] is presented. The pinch plasma is modeled as a foam-like medium saturated with toroidal "magnetic bubbles" produced by the development of surface m=0 Rayleigh-Taylor and MHD instabilities. As the bubbles converge to the pinch axis, their magnetic energy is converted to thermal energy of the plasma through pdV work. Explicit formulas for the average dissipation rate of this process and the corresponding contribution to the resistance of the load, which compare favorably to the experimental data and simulation results, are presented. The possibility of using this enhanced (relative to Ohmic heating) dissipation mechanism to power novel plasma radiation sources and produce high K-shell yields using long current rise time machines is discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874192
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  • 9
    Electronic Resource
    Electronic Resource
    Analyzing spatially resolved line spectra emitted by Z pinches (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3399-3404 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatial profiles of key physical variables such as electron temperature and density are crucial in determining the overall radiating efficiency of a Z pinch as well as the emitted photon energy distribution. The present work uses spatially resolved x-ray lines emitted from shots taken on the 4 MA Double EAGLE generator [C. Deeney et al., Phys. Rev. A 44, 6762 (1991)] at Maxwell Physics International to infer such profiles. The loads were arrays of 15 wires consisting of 95% Al, 5% Si, producing nearly 50 kJ of K-shell radiation with relatively long pulsewidths of 41–43 ns. It is found that the spatial profile of the He-like intercombination to resonance line ratio is critically affected by self-absorption and re-emission (scattering) of resonance line photons emitted from the hot, dense interior of the pinch. This ratio cannot be correctly interpreted without taking the scattering into account. Also, at densities somewhat lower than those achieved by these pinches, this line ratio becomes more temperature than density dependent. The inferred temperature gradient is much less steep than that which had been diagnosed previously for a pinch emitting a much shorter x-ray pulsewidth of 13 ns. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874203
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetics and dynamics of the initial adsorption of nitric oxide on Ir(111) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8362-8375 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction of nitric oxide (NO) with an Ir(111) surface has been studied with supersonic molecular beam techniques and electron energy loss spectroscopy. Initial adsorption probability S0, measurements as a function of incident kinetic energy Ei, surface temperature Ts, and angle of incidence θi reveal that separate mechanisms govern adsorption at low and high kinetic energy. This distinction is reflected in measurements of the initial molecular adsorption probability where a decrease in the value of S0 with increasing Ts (between 77 and 300 K) is observed at low kinetic energy (Ei〈0.45 eV), but no surface temperature dependence is detected at high kinetic energy in this temperature range. We present a model describing both the molecular and dissociative chemisorption of NO on Ir(111). At low kinetic energy, NO adsorbs initially as a physically adsorbed species. From this state, desorption to the gas phase or conversion to a molecularly chemisorbed state on the surface are competing processes which depend on surface temperature. The molecularly chemisorbed state is the precursor to dissociation for elevated surface temperatures. At high kinetic energy, NO adsorption occurs directly into the molecularly chemisorbed well, with the probability of trapping as a physically adsorbed species near zero and with undetectable direct dissociation. Indeed, after exposure of the Ir(111) surface at 77 K to a high kinetic energy (1.3 eV) beam, surface vibrational spectroscopy measurements show only features attributable to molecularly chemisorbed NO. The success of this model in describing our measurements is demonstrated by the separate calculation from low and high kinetic energy data of rate constants corresponding to forward and reverse conversion from the molecularly chemisorbed well. Additionally, we discuss attempts to promote dissociation on the surface with vibrational energy and with a combination of translational and surface thermal energy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472691
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