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  • Articles  (121)
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  • 1
    Electronic Resource
    Electronic Resource
    Negative electron affinity based vacuum collector transistor (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3042-3044 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the operation of a vacuum collector–semiconductor transistor based on negative electron affinity cold cathode technology. The unique aspect of this transistor is that the collector is separated from the emitter-base junction by a vacuum drift region, yielding an intrinsic collector capacitance which is an order of magnitude lower than that for conventional bipolar transistors. The collector charging time is thus proportionally smaller. Transport in the vacuum drift region is truly ballistic and depends only on the collector-base bias, enabling a wide range of device concepts which are impossible or impractical in conventional transistors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350990
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular beam studies of H2 and D2 dissociative chemisorption on Pt(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5240-5246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular beam techniques have been utilized to measure the dissociative chemisorption probability at zero surface coverage S0 for D2(H2) on Pt(111) as a function of initial energy Ei, angle of incidence θi, surface temperature Ts, isotopic mass and nozzle temperature Tn. S0 shows a large increase with translational energy, but no threshold in Ei, a peaking at θi=0°, and an independence with Ts, isotope and Tn. These results are interpreted in terms of direct dissociative chemisorption on the Pt(111) terraces. The dynamical picture that emerges is that although there is no significant barrier to dissociation along the minimum energy path, barriers do exist along nonoptimal reactive trajectories. Thus, the "translational activation'' and other dynamical observations are intimately related to the multidimensional aspects of the dissociative potential energy surface. Some aspects of the dissociative chemisorption, however, still seem somewhat surprising within this general description.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459669
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  • 3
    Electronic Resource
    Electronic Resource
    The sticking of O2 on a Pt(111) surface (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4381-4395 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports detailed molecular beam measurements of the sticking coefficient at zero coverage for O2 on a Pt(111) surface as a function of initial energy (Ei), angle of incidence (θi), and surface temperature (Ts). Under most conditions the sticking coefficient measures the probability for dissociative chemisorption. These results demonstrate that both precursor mediated and quasi-direct dissociation can be observed, depending upon the initial conditions. The quasi-direct process is revealed by a step increase in the sticking with Ei. This feature scales intermediately between Ei and the normal component En, and is weakly dependent on Ts. The precursor mediated sticking is well described by standard precursor kinetic models. At low Ei and Ts, sticking measures trapping into a molecularly adsorbed state. This trapping decreases more rapidly with Ei than anticipated from simple models and scales intermediately between Ei and En. The sticking results are discussed in terms of likely dynamic processes occurring on a potential energy surface which contains an intermediate molecularly adsorbed species formed by charge transfer from the metal to the O2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454824
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  • 4
    Electronic Resource
    Electronic Resource
    Laser IR polarization spectroscopy at surfaces (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3322-3330 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel form of laser polarization spectroscopy is described which allows vibrational spectra of submonolayers of some adsorbates on metal surfaces to be observed. As a demonstration of its potential, spectra for CO adsorbed on a Pt(111) single crystal were obtained using a continuously tunable pulsed IR laser. The temperature dependence of the lineshape for the CO stretch in an on-top adsorption site was measured and interpreted in terms of exchange-coupling dephasing. Since sensitivity achieved with this spectroscopy is not yet as high as that obtainable with conventional IRRAS, the issue of noise sources and sensitivity in the laser spectroscopy is examined in some detail, and possibilities for future enhancements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453926
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  • 5
    Electronic Resource
    Electronic Resource
    Development of a dc low pressure D− surface-conversion source using a 10-cm-diam solid barium converter : Proceeding of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2705-2707 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A D− surface-conversion source using a solid barium converter is designed for steady-state operation to produce 200 mA of D−. A similar ion source of twice the size as the one discussed here will meet the requirements set by the present US-ITER neutral beam injector design. Among the possible types of ion sources being considered for the US-ITER neutral beam design, the barium converter surface-conversion source is the only kind that does not use cesium in the discharge. This absence of cesium will minimize the number of accelerator breakdowns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142829
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  • 6
    Electronic Resource
    Electronic Resource
    rf driven multicusp H− ion source (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 100-104 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An rf driven multicusp source capable of generating 1-ms H− beam pulses with a repetition rate as high as 150 Hz has been developed. This source can be operated with a filament or other types of starter. There is almost no lifetime limitation and a clean plasma can be maintained for a long period of operation. It is demonstrated that rf power as high as 25 kW could be coupled inductively to the plasma via a glass-coated copper-coil antenna. The extracted H− current density achieved is about 200 mA/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142315
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  • 7
    Electronic Resource
    Electronic Resource
    Particle reflection and TFTR neutral beam diagnostics : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4523-4526 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Determination of two critical neutral beam parameters, power and divergence, are affected by the reflection of a fraction of the incident energy from the surface of the measuring calorimeter. On the TFTR Neutral Beam Test Stand, greater than 30% of the incident power directed at the target chamber calorimeter was unaccounted for. Most of this loss is believed due to reflection from the surface of the flat calorimeter, which was struck at a near grazing incidence (12°). Beamline calorimeters, of a "V''-shape design, while retaining the beam power, also suffer from reflection effects. Reflection, in this latter case, artificially peaks the power toward the apex of the "V,'' complicating the fitting technique, and increasing the power density on axis by 10%–20%; an effect of import to future beamline designers. Agreement is found between measured and expected divergence values, even with 24% of the incident energy reflected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143709
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  • 8
    Electronic Resource
    Electronic Resource
    Improvement of the lifetime of radio frequency antenna for plasma generation : The 8th international conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1134-1136 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: At Lawrence Berkeley National Laboratory different antenna protection schemes have been investigated for the radio frequency-driven multicusp ion source. It was found that the antenna lifetime can be greatly enhanced by an additional shielding, which consists of porcelain, quartz or boron nitride. Different antenna configurations and their influence on the plasma generation will be discussed. Antenna life time greater than 500 hours continuous wave operation has been demonstrated in hydrogen plasma using a novel quartz antenna design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150407
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  • 9
    Electronic Resource
    Electronic Resource
    Development of the radio frequency driven H− ion source for the National Spallation Neutron Source : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 962-964 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ion source for the 1 MW National Spallation Neutron Source (NSNS) is required to provide 35 mA of H− beam current (1 ms pulses at 60 Hz) at 65 keV with a normalized root-mean-square emittance of 〈0.2 pi mm mrad. The same ion source should be able to produce 70 mA of H−at 6% duty factor when the NSNS is upgraded to 2 MW of power. For this application, a radio-frequency driven, magnetically filtered multicusp source is being developed at Lawrence Berkeley National Laboratory. The design of this R and D ion source, which is equipped with a cesium dispenser-collar, a fast ion beam prechopper (rise times 〈100 ns) and a strong permanent-magnet insert for electron deflection, will be presented.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148703
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  • 10
    Electronic Resource
    Electronic Resource
    Ion source electrode biasing technique for microsecond beam pulse rise times : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1060-1062 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Heavy ion fusion (HIF) induction accelerators require ion sources that can deliver intense heavy ion beams with low emittance. The typical pulse length is 20 μs with a rise time less than 1 μs and a repetition rate of 10 Hz. So far, the surface ionization sources have been used in most HIF induction linac designs. However, there are other ions of interest to HIF (e.g., Hg, Xe, Rb, Ar, and Ne) which cannot be produced by the surface ionization sources, but rather by volume ion sources. In this paper, we describe an experiment that uses a multicusp source with a magnetic filter to produce beam pulses that have a rise time in the order of 1 μs. By applying a positive biasing pulse on the plasma electrode with respect to the source body, the positive plasma ions can be temporarily repelled from the neighborhood of the extraction aperture, leading to a suppression of the ion beam. As the bias is removed, positive ions flow to the extraction region, enabling a fast-rising beam pulse. The beam current pulses show that there are two distinct groups of ions. An initial fast current rise time (〈2 μs) corresponding to ions originating from within the magnetic filter region followed by a second group of ions with a longer rise time (10–20 μs) originating from the plasma bulk region. Proper positioning of the filament cathode and the magnetic filter field relative to the extraction aperture was found to be critical. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148710
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