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  • American Institute of Physics (AIP)  (12)
  • Paleontological Society  (1)
  • 1995-1999  (13)
  • 1
    Electronic Resource
    Electronic Resource
    Microwave proton source development for a high-current linac injector (invited)a) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1296-1301 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Powerful cw proton linear accelerators (100 mA at 0.5–1.0 GeV) are being proposed for spallation neutron-source applications. A 75-keV, 110-mA dc proton injector using a microwave ion source is being tested for these applications. It has achieved 80-keV, 110-mA hydrogen-ion-beam operation. Video and dc beam-current toroid diagnostics are operational, and an EPICS control system is also operational on the 75-keV injector. A technical base development program has also been carried out on a 50-keV injector obtained from Chalk River Laboratories, and it includes low-energy beam transport studies, ion source lifetime tests, and proton-fraction enhancement studies. Technical base results and the present status of the 75-keV injector will be presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146701
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  • 2
    Electronic Resource
    Electronic Resource
    Production of high-brightness continuous wave proton beams with very high proton fractions (abstract)a) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1239-1239 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article demonstrates a new technique to significantly enhance the proton fraction of an ion beam extracted from a plasma ion source. We employ a magnetically confined microwave driven source, though the technique is not source specific and can probably be applied equally effectively to other plasma sources such as Penning and multicusp types. Specifically, we dope the plasma with about 1% H2O, which increases the proton fraction of a 45 keV 45 mA beam from 75% to 90% with 375 W 2.45 GHz power to the source and from 84% to 92% for 500 W when the source is operated under nonresonant conditions. Much of the remaining fraction of the beam comprises a heavy mass ion we believe to be N+ impurity ions resulting from the conditions under which the experiments were performed. If so, this impurity can easily be removed and much higher proton fractions could be expected. Preliminary measurements show the additive has no adverse effect on the emittance of the extracted beam, and source stability is greatly improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147239
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  • 3
    Electronic Resource
    Electronic Resource
    Development of a 130-mA, 75-kV high voltage column for high-intensity dc proton injectors : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1017-1019 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reliable high-voltage (HV) column has been developed for dc proton injectors with applications to high-intensity cw linacs. The HV column is coupled with a microwave-driven plasma generator to produce a 75-keV, 110-mA dc proton beam. Typical proton fraction from this source is 85%–90%, requiring the HV column and accelerating electrodes to operate with a 130-mA hydrogen-ion beam current. A glow-discharge, which was caused by the ion source axial magnetic field, was initially observed in the HV column. This problem was solved by scaling the electron production processes, the magnetic field, and the HV column pressure into a favorable regime. A subsequent 168 h reliability run on the 75-keV injector showed that the ion source (plasma generator and HV column) has 〉98% beam availability. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148707
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  • 4
    Electronic Resource
    Electronic Resource
    Diffraction of high-energy synchrotron radiation (invited) (abstract) : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1614-1614 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Diffraction of high-energy synchrotron radiation at energies above 100 keV combines advantages of conventional x-ray diffraction and neutron diffraction. For hard x rays absorption in matter is weak with typical mean free paths of several millimeters. Bulk properties are studied on large samples. With a three-crystal diffractometer an excellent k-space resolution of about 10−5 A(ring)−1 transversal and 10−4 A(ring)−1 longitudinal is achieved. In this contribution the particularities of hard x rays, the instrumental setup, and the k-space resolution are discussed and presented. The potential of the new method will be demonstrated on two examples: magnetic diffraction from MnF2 and the structural phase transition of SrTiO3. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146465
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  • 5
    Electronic Resource
    Electronic Resource
    Status report on a dc 130 mA, 75 keV proton injector (invited) : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1003-1008 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 110 mA, 75 keV dc proton injector is being developed at Los Alamos. A microwave proton source is coupled to a two solenoid, space-charge neutralized, low-energy beam transport (LEBT) system. The ion source produces 110 mA proton current at 75 keV using 600–800 W of 2.45 GHz discharge power. Typical proton fraction is 85%–90% of the total extracted ion current, and the rms normalized beam emittance after transport through a prototype 2.1 m LEBT is 0.20 (πmm mrad). Beam space-charge neutralization is measured to be 〉98% which enables the solenoid magnetic transport to successfully match the injector beam into a radio-frequency quadrupole. Beam simulations indicate small emittance growth in the proposed 2.8 m low-energy demonstration accelerator LEBT. The LEBT also contains beam diagnostics, steering, and a beam deflector for variable duty factor and accelerator fast protect functions. The injector beam availability status is also discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148706
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  • 6
    Electronic Resource
    Electronic Resource
    Distribution of SiO2 precipitates in large, oxygen rich Czochralski-grown silicon single crystals after annealing at 750 °C (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 553-562 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The defects due to oxygen precipitation in Czochralski grown silicon single crystals annealed for 216 h at 750 °C and with oxygen concentration varying between 18 and 12×1017 atoms per cm3 (according to DIN 50438) were studied by means of small angle neutron scattering and γ-ray diffractometry probing the same volume elements in the sample. The size and the shape of the SiO2 precipitates were determined by means of small angle neutron scattering. In the center of the disk-shaped sample of 10 cm diameter one finds spherical precipitates with a radius of ≈20 A(ring), at the border the precipitates are of plate-like shape, ≈146×146×41 A(ring) in dimension. The k-space distribution of the diffuse scattering caused by the strain field of the SiO2 precipitates has been determined by means of a double-crystal diffractometer and 316 keV γ radiation. Modeling with Huang and Stokes–Wilson theory suggests that the relatively small SiO2 precipitates are loosely bound in larger clusters with a radius of ≈2000 A(ring) in which the crystal matrix is strongly distorted. With the γ-ray diffractometer operated in the single-crystal mode the thickness dependence of the integrated reflecting power was measured from which the static Debye–Waller factor for the 2 2 0 reflection is determined using statistical dynamical theory. The results confirm qualitatively the cluster model. In the center of the sample the size of the precipitates could be calculated by additional measurement of the static Debye–Waller factor of the 4 4 0 reflection. The result is in excellent agreement with the small angle neutron scattering data. Combining all the experimental data taken in the oxygen rich center of the annealed silicon crystal the average distance between the centers of the SiO2 precipitates in the clusters is ≈80 A(ring) and the distance between the large clusters is ≈40 000 A(ring). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359039
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  • 7
    Electronic Resource
    Electronic Resource
    Resonant Raman scattering in hexagonal GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2404-2406 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed resonant Raman scattering in hexagonal GaN using discrete laser lines in the violet and UV spectral range for optical excitation. To tune the energetic position of the fundamental gap E0 of GaN relative to the exciting photon energy the sample temperature was varied between 77 and 870 K. Analyzing both Stokes and anti-Stokes Raman spectra, the resonance profiles for Fröhlich-induced one-E1(LO) and two-E1(LO) phonon scattering could be deduced, covering the energy range from 0.5 eV below the E0 gap up to the gap energy. The strength of deformation-potential scattering by the A1(TO) mode was used as an internal reference. For excitation slightly above the E0 gap energy E1(LO) multiphonon scattering up to the fourth order was observed, which reflects the stronger polarity of the Ga-N bond as compared to conventional III-V semiconductors. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116148
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  • 8
    Electronic Resource
    Electronic Resource
    Photoluminescence of residual transition metal impurities in GaN (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1140-1142 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A large number of epitaxial GaN samples as well as AlN ceramics have been studied by photoluminescence (PL) and PL excitation spectroscopy. In addition to the PL of residual iron, two new bands with zero-phonon-lines at 0.931 and 1.193 eV have been observed frequently in GaN. An analysis of the PL bands indicates that they arise from internal transitions within the 3d shell of residual vanadium and chromium impurities. The chromium PL has also been observed in polycrystalline AlN ceramics. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114987
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  • 9
    Electronic Resource
    Electronic Resource
    Production of high-brightness continuous wave proton beams with very high proton fractionsa) (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1642-1645 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article demonstrates a new technique to significantly enhance the proton fraction of an ion beam extracted from a plasma ion source. We employ a magnetically confined microwave driven source, though the technique is not source specific and can probably be applied equally effectively to other plasma sources such as Penning and multicusp types. Specifically, we dope the plasma with about 1% H2O, which increases the proton fraction of a 45 keV 45 mA beam from 75% to 90% with 375 W 2.45 GHz power to the source and from 84% to 92% for 500 W when the source is operated under nonresonant conditions. Much of the remaining fraction of the beam comprises a heavy mass ion we believe to be N+ impurity ions resulting from the conditions under which the experiments were performed. If so, this impurity can easily be removed and much higher proton fractions could be expected. Preliminary measurements show the additive has no adverse effect on the emittance of the extracted beam, and source stability is greatly improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146908
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  • 10
    Electronic Resource
    Electronic Resource
    Evaluation of a simple method for chopping Penning surface-plasma source H− beams (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1024-1027 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Accumulator rings proposed for use in high-intensity spallation-neutron sources require a chopped beam with ∼100-ns-wide particle-free gaps at 1–2 MHz rates, with fall and rise times ≤20 ns. Chopping the beam directly in the ion source may be an attractive way to provide the desired beam structure. Previous measurements showed that placing a grounded collar in the drift region just before the emission aperture lowers the e−/H− ratio in the Penning surface-plasma source H− beam. We electrically isolated the collar and biased it to modulate the extracted H− current. Positive collar bias decreases the H− beam by up to 90%. The fastest H− current fall and rise times achieved to date are 400 ns and 2 μs, respectively. The current fall time is close to the 300-ns pulser rise time. The current rise time is considerably longer than the 500-ns pulser fall time. Negative collar bias lowers the H− beam by up to 50%. Simulations indicate that the beam time structure will be preserved in transport from the ion source to the radio-frequency quadrupole entrance. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146039
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