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  • 1
    Electronic Resource
    Electronic Resource
    High resolution time-of-flight analysis of photon stimulated ion desorption from chemically treated silicon surfaces (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4156-4160 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The native oxide, thermally oxidized and hydrofluoric acid rinsed surfaces of Si(100) have been characterized by photon stimulated ion desorption (PSD), and both photoelectron and Auger electron spectroscopies. The only species detected by PSD were H+ ions with different kinetic energies. Low kinetic energy H+ ions were detected only from the HF rinsed surfaces presumably arising from scission of Si—H bonds while higher kinetic energy ions attributed to adsorbed hydrocarbon dissociation were observed for all of the surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352224
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  • 2
    Electronic Resource
    Electronic Resource
    High-purity ion beam production at high current densities with a liquid-helium-cooled series-field-coil extraction ion diode (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2926-2938 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments are described in which a high-purity, high-power (0.15 TW, 1 MeV) proton beam is generated from an ion source consisting of H2 gas frozen onto a liquid-helium-cooled copper anode at 4.2 K in a series-field-coil extraction diode on the 0.7 TW HydraMITE-II accelerator. Peak anode proton current densities of 2 kA/cm2 were measured. This current density is a factor of 100 higher than those obtained in previous liquid-helium-cooled cryogenic diode experiments on small accelerators and is in the range required for high-power ion beam applications. Thomson parabola, Faraday cup, and carbon activation measurements indicate an ion beam proton fraction close to 100% for the cryogenic source, compared to 50–70% for the standard hydrocarbon anode tested. The cryogenic proton source is believed to consist of no more than a few monolayers of molecular hydrogen. The hydrogen-coated cryogenic anode shows a faster initial anode turn-on than other materials. However, source-limited emission from the thin hydrogen layer results in a somewhat longer current risetime, reduced ion diode efficiency, lower proton current enhancement over the Child–Langmuir limit, and a proton spectrum of lower average energy than for the hydrocarbon anode. Techniques to overcome these limitations are discussed. Cryogenic ion sources consisting of frozen N2, CH4, and Ne have also been studied. In each case, high intensity beams consisting predominantly of components of the refrigerated gas were produced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349317
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  • 3
    Electronic Resource
    Electronic Resource
    Lithium niobate stress gauge current diagnostic for noninductive measurement of fast-rise-time multimegampere currents (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4917-4928 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate modeling of load behavior in Z-pinch plasma radiation sources driven by high-current generators requires the measurement of fast-rise-time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B-dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by high dI/dt. In this paper, we describe the use of large-signal, nanosecond-time-resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressure B2/2μ0=μ0I2/8π2r2 generated at radius r by a current I flowing in a radial transmission line. Current measurements have been performed at radius r=2.54×10−2 m on Sandia National Laboratories' Proto-II (10 TW) and SATURN (30 TW) gas puff Z-pinch experiments with maximum currents of 10.1 MA and dI/dt to 2.1×1014 A/s. Comparisons with Faraday rotation and B-dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y-cut lithium niobate stress gauge on a pure tungsten electrode, current densities up to I/2πr=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X-cut quartz piezoelectric element and a tungsten-sapphire electrode impedance stack.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347077
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  • 4
    Electronic Resource
    Electronic Resource
    Single-event, energy-resolved, Auger–electron, multiple-ion coincidence mass spectroscopy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9200-9202 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An experimental method is described that is directed at monitoring the creation and decay of core hole states in molecules from state-to-state. Data in the form of a coincidence map are presented and analyzed for the case of nitrous oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459212
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  • 5
    Electronic Resource
    Electronic Resource
    Core-hole excited states of H2O: Symmetries and relative oscillator strengths (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5915-5918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Tunable and polarized soft x-ray radiation was used to excite core electrons of H2O. Angle-resolved proton yields were measured by retarding potential analyzers at 0° and 90° with respect to the polarization vector of the radiation. The ability of angle-resolved detection to reveal hidden resonances in rich molecular spectra is demonstrated, and the anisotropy parameter obtained from the two ion yields identifies the symmetries and the relative oscillator strengths of the core-hole excited states in the near-edge region of the spectrum. The analysis of the data substantiates the validity of the axial recoil approximation and provides evidence for ultrafast dissociation. Comparisons with the results of theoretical calculations are made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463985
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic decay of core hole excited states in molecular oxygen (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2169-2175 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron energy spectra characterizing the relaxation of molecular oxygen from different core hole excited states are reported. By using monochromatic synchrotron radiation, spectra are obtained with excitation at the π* and σ* resonances and at various energies above the ionization threshold. The spectra obtained with excitation above threshold are very similar and result from Auger decay. The spectra obtained at the σ* resonance result from spectator autoionization, and those for the π* resonance result from both spectator and participator autoionization. The σ* resonance is broadened by spectral congestion, and the autoionization spectra indicate the presence of three components. Configurations and states produced by the electronic decay are identified, and a correlation between spectator screening and term values is documented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459048
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  • 7
    Electronic Resource
    Electronic Resource
    Angular dependence of photofragments from K-shell excited N2 and O2: Photoabsorption anisotropy and excited state symmetry (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7936-7945 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The symmetry of excited states reached by photoexcitation of K-shell electrons of N2 and O2 is identified from the fragmentation anisotropy. For each molecule, ion yield excitation spectra were obtained at 90°, 54.7°, and 0° relative to the axis of soft x-ray polarization. The degree of polarization of the synchrotron radiation was determined experimentally. From this determination and the angular dependence of the ion yield, the photoabsorption anisotropy parameter β is obtained as a function of photon energy. Variations in the β spectra are discussed in terms of previously assigned spectral features and are compared with other experimental results. A comparison also is made with theoretical calculations, which are available for the case of N2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459323
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  • 8
    Electronic Resource
    Electronic Resource
    Origin of the blue bands in the luminescence spectrum of core excited O2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2183-2188 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular oxygen was excited by 1.5–3.0 keV electrons. Luminescence spectra from the decay products of K-shell excitation were obtained at high resolution (bandwidth of 0.3 A(ring)). With this resolution it was possible to identify and assign the observed lines to transitions from highly-excited Rydberg states of O+ and O fragments. These states appear to result from inner valence two-hole states and three-hole, one-electron states produced by Auger decay of the core hole in molecular oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463110
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  • 9
    Electronic Resource
    Electronic Resource
    Measurement of radiation symmetry in Z-pinch-driven hohlraums : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2173-2181 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Z-pinch-driven hohlraum (ZPDH) [J. H. Hammer et al., Phys. Plasmas 6, 2129 (1999)] is a promising approach to high yield inertial confinement fusion currently being characterized in experiments on the Sandia Z accelerator [M. E. Cuneo et al., Phys. Plasmas 8, 2257 (2001)]. Simulations show that capsule radiation symmetry, a critical issue in ZPDH design, is governed primarily by hohlraum geometry, dual-pinch power balance, and pinch timing. In initial symmetry studies on Z without the benefit of a laser backlighter, highly-asymmetric pole-hot and equator-hot single Z-pinch hohlraum geometries were diagnosed using solid low density foam burnthrough spheres. These experiments demonstrated effective geometric control and prediction of polar flux symmetry at the level where details of the Z-pinch implosion and other higher order effects are not critical. Radiation flux symmetry achieved in Z double-pinch hohlraum configurations exceeds the measurement sensitivity of this self-backlit foam ball symmetry diagnostic. To diagnose radiation symmetry at the 2%–5% level attainable with present ZPDH designs, high-energy x rays produced by the recently-completed Z-Beamlet laser backlighter are being used for point-projection imaging of thin-wall implosion and symmetry capsules. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455002
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  • 10
    Electronic Resource
    Electronic Resource
    Rotational distributions of molecular ions following core excitation and decay (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5239-5241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational distribution in the N2+ (B) state produced by core excitation and decay is reported for three different core excitation energies. In contrast to the case of valence excitation, the rotational branching ratios do not exhibit a significant dependence on excitation energy. This similarity is attributed to the uniformly high kinetic energies of the emitted electron for the three cases and provides evidence for the production of singly charged molecular ions in the core ionization continuum through an interchannel coupling mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465064
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