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  • 1
    Electronic Resource
    Electronic Resource
    In-plane effective mass of electrons in InGaAs/InP quantum wells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2828-2830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measured the in-plane effective mass for electrons in multiquantum wells in InGaAs/InP by the Shubnikov–de Haas effect. We varied the well width from 8.6 down to 2.3 nm where the enhancement of the effective mass is predicted to be very pronounced. The electron concentration was in the range of 3×1011 cm−2, so that band filling can be neglected. The variation of the effective mass from 0.045 to 0.067m0 is in accordance with current theories. We discuss the effect of the interface roughness and ionized impurities on the scattering times as found from our experiments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358694
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  • 2
    Electronic Resource
    Electronic Resource
    Measurements and code comparison of wave dispersion and antenna radiation resistance for helicon waves in a high density cylindrical plasma source (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 703-712 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Helicon wave dispersion and radiation resistance measurements in a high density (ne(approximate)1019−1020 m−3) and magnetic field (B〈0.2 T) cylindrical plasma source are compared to the results of a recently developed numerical plasma wave code [I. V. Kamenski and G. G. Borg, Phys. Plasmas 3, 4396 (1996)]. Results are compared for plasmas formed by a double saddle coil antenna and a helical antenna. In both cases, measurements reveal a dominance of the m=+1 azimuthal mode to the exclusion of most other modes; in particular, no significant m=−1 mode was observed. The helical antenna, designed to launch m〈0 and m〉0 modes in opposite directions along the field, resulted in an axially asymmetric discharge with very little plasma on the m〈0 side of the antenna. For both antennas, good agreement of the antenna radiation resistance and wave dispersion with the model was obtained. It is concluded that unshielded antennas formed from current loops with an important |m|=1 component for the conditions of our experiment, couple most of their power to the m=+1 helicon mode and thus have negligible parasitic, nonhelicon plasma loading. This result greatly simplifies calculations of power balance in these sources by identifying the helicon as the mode by which energy is transferred to the plasma. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873307
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  • 3
    Electronic Resource
    Electronic Resource
    Projection x-ray microscope powered by highly charged ions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 204-209 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recombination of slow highly charged ions at the surface of a target foil can be used as a source of x rays for a projection x-ray microscope. In a first test of this concept, a low emittance beam of Ar18+ and Ar17+ ions from an electron beam ion trap was focused with einzel lenses to a 20 μm full width at half maximum spot on a beryllium target foil. The 3 keV x rays from radiative deexcitation of the ions were used to obtain a magnified image of an electroformed nickel mesh with 20 μm resolution by projection onto a CCD camera. Prospects for substantial improvements in resolution and intensity are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148496
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  • 4
    Electronic Resource
    Electronic Resource
    Distinction between multicharged ion species with equal q/m (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3499-3502 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a new technique for selective, highly sensitive, absolute detection of different multiply charged ion species with equal charge-to-mass ratios in mixed multicharged ion beams. This is achieved by exploiting the statistics of potential electron emission as induced by the ion beams on a clean metal surface. The applicability of the method is illustrated by way of different practical examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144274
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  • 5
    Electronic Resource
    Electronic Resource
    Proton beam targets shot on PBFA-II : 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. 4779-4781 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In recent proton beam experiments on PBFA-II, foam-filled gold targets and gas-filled spherical exploding pushers were shot as physics targets. Surrounding these targets were gold foils used to characterize the beam. The target fabrication and characterization are presented in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143560
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  • 6
    Electronic Resource
    Electronic Resource
    Confinement in a cryogenic penning trap of highest charge state ions from EBIT (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3472-3478 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The retrapping of highly charged Xe44+ and Th68+,72+ ions extracted from an "electron-beam ion trap'' (EBIT) is demonstrated after injection of the ions into RETRAP, a cryogenic Penning trap (up to 6 T magnetic field) currently with an open cylinder design. Ion extraction in a short pulse (5–20 μs) from EBIT, essential for efficient retrapping, is employed. The ions are slowed down upon entering a deceleration tube mounted above the trap within the magnetic field. The potential is then rapidly (100 ns) decreased, enabling low-energy ions to enter the trap. Capture efficiencies up to 25% are observed via detection of the delayed ion release pulse with a detector below the trap. Signal voltages induced in a tuned circuit due to single and multiple ions have been observed by tuning the ion resonant axial oscillation frequencies for different ions. Results from transporting and retrapping of the ions, as well as their detection, are described and the trapping efficiency is discussed. The motivation for these studies is to cool the trapped very highly charged ions to low temperatures (〈4 K) in order to perform ultrahigh-resolution precision spectroscopy, collision studies at ultralow energies, and to observe phase transitions in Coulomb clusters of highly charged ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144525
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  • 7
    Electronic Resource
    Electronic Resource
    Modeling the ion-source performance of an electron-beam ion trap (invited) : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2806-2811 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several key features of the electron-beam ion trap (EBIT) enable it to provide superior ion-source performance for many applications requiring ultra-high-charged ions. This paper briefly reviews these features and the operating conditions in the existing EBITs. The present performance of the EBIT as an ion source is demonstrated by producing and extracting ions up to Th80+ and U70+ at microsecond-wide ion beam pulses of about 104 ions per second. Using as examples the production of U92+, U90+, and Dy66+, modeling results are presented to show how the fundamental processes limit the quality and quantity of ions that can be obtained from an upscaled EBIT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142812
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  • 8
    Electronic Resource
    Electronic Resource
    Anisotropic effective mass and scattering of electrons in mismatched heteroepitaxial films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6542-6549 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InP layers grown epitaxially on silicon substrates show a pronounced anisotropy of the transverse magnetoresistance. We use this effect to study the ensuing anisotropy of the effective mass and scattering mechanisms of electrons. We investigated samples with an electron concentration from 7×1016 to 9.6×1017 cm−3 at temperatures ranging from 4.2 to 30 K in magnetic fields of up to 15 T. The sample with the lowest electron concentration showed an anisotropic negative magnetoresistance which we attribute to weak localization. This allows the characteristic times for inelastic scattering (coherence time) and for spin–orbit interaction to be determined. For the InP layers on Si of higher electron concentration we measured for the first time Shubnikov-de Haas oscillations, showing again anisotropy of the effective mass and of the Dingle temperature. We quantitatively ascribe differences from the bulk values to biaxial mechanical strain, distorting the Fermi sphere of bulk material to an ellipsoid. We assume that the observed anisotropies are due to a preferential orientation of crystal defects as a result of differences in the thermal expansion coefficient of the InP film and the Si substrate. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370159
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  • 9
    Electronic Resource
    Electronic Resource
    Extraction of highly charged ions (up to 90+) from a high-energy electron-beam ion trap (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 30-35 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The extraction of high-Z high-charge-state ions up to U90+ from a high-energy electron-beam ion trap, the SuperEBIT at Lawrence Livermore National Laboratory, is reported. The SuperEBIT provides a 240 mA electron beam with up to 200 keV of energy. Depending on the operating conditions (pulsed, continuous) and charge state, the number of ions extracted from the SuperEBIT varies between 102 and 105 ions per second under the tested conditions. The ions produced in SuperEBIT are extracted at potentials ranging from 0.5 to 20 keV (continuously variable) to provide highly charged low-emittance ion beams with energies between a few keV and several MeV. The performance of the SuperEBIT as an ion source is described and aspects for future developments and potential applications are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1419216
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  • 10
    Electronic Resource
    Electronic Resource
    Diffusion coefficients in anisotropic fluids by ESR imaging of concentration profiles (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3387-3395 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report on the use of ESR imaging for determining the translational diffusion constants of typical ESR spin probes in ordered and isotropic solvents. A discussion is given for a Fourier deconvolution method for determining the correct concentration profile if there is more than one hyperfine line in the spectrum of the radical as well as a spatial dependence of the spectrometer sensitivity. A simple but approximate subtraction deconvolution method is also presented. The diffusion constants for 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONE) in the nematic and isotropic phases of the liquid crystal p-pentylbenzylidine-p-butylanaline (5,4) were determined. In the isotropic phase the diffusion coefficient is isotropic (D=2.5×10−6 cm2 s−1, at 50 °C), while in the nematic phase it was found to be mildly anisotropic. The diffusion coefficients for motion perpendicular and parallel to the director axis in the nematic phase are respectively, D⊥ =9.0×10−7 cm2 s−1, D(parallel) =6.4×10−7 cm2 s−1 at 27 °C. This is interpreted in terms of some smectic-like character in the nematic phase of 5,4. Possible improvements in the technique are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450221
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