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  • 11
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 2.45 GHz electron cyclotron resonance (ECR) ion source with a single mode resonator is being developed to produce high efficient single charged ion beams from exiguous gaseous elements. The source is intended to produce short and long half-life radioactive ion beams as well as stable ion beams for low and high energy experiments at ISAC [J. M. Poutissou, Proceedings of the ISAC Workshop (1994)]. It is obvious that for the radioactive ion beam production, the gas and ion transient time and the overall ionization efficiency are the most important parameters. The transient time is measured using ultrafast peizoelectric gas valve which could operate up to a frequency of 2 kHz. A unique feature of the source is that the plasma chamber is considerably smaller (∼170 times) than its resonance cavity in order to minimize the transient time. Quartz tubes with various diameters (5–20 mm) and 80 mm long are tested as the plasma chamber and the results are discussed. The effect of the transfer tube length, which links the target and the ion source on the transient time is also described. An axially symmetric five electrode extraction system containing three multiaperture electrodes was used to extract the beam. The source, including ECR coils and extraction system is placed in the middle of a 60 cm×60 cm×90 cm vacuum box to simulate the ISAC target module conditions. The preliminary results of the molecular and ion transient time studies, beam efficiency studies are also presented in this article. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3324-3327 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report electrical measurements on structures generated by δ doping the AlGaAs barriers of a GaAs quantum well. These structures are made unique by quantum size effects that occur both in the δ-doped barrier and in the GaAs well. Both the Hall-effect and capacitance-voltage measurements reveal that high-density, 4×1012 cm−2, two-dimensional electron gas forms in the well along with good mobility. We fabricate field-effect transistors with this structure to obtain transconductances of 300 mS/mm.
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  • 13
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 2.45 GHz electron cyclotron resonance ion source has been designed and built to ionize radioactive atoms and produce single charged ion beams for the isotope separator and accelerator at TRIUMF. The source is characterized by its short axial length (8 cm) and the small pair of magnetic coils (diam=φ26 cm) placed adjacent to the source cavity. A small diameter quartz tube is inserted in the cavity to confine the plasma to a small volume and to shorten total ion transient time for the exotic gaseous elements with short and intermediate half life. The computer code POISSON is used to design the magnetic coils. A three-electrode extraction system simulated with the code IGUNE is used to study the beam extraction efficiency. In this article the design of the source, extraction system, and the preliminary results on beam emittance and energy spread are presented; the results on ion transient time, ionization efficiency, and beam extraction efficiency are presented in a separate article. © 2000 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1191-1193 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier heights in the epitaxial (100) CoGa/n-(100) GaAs diodes were studied by the I-V and internal photoemission methods. Diodes of these epitaxial contacts were shown to exhibit good rectifying behaviors and the forward current was found to follow the thermionic emission theory. Using the temperature dependence of the barrier heights, we show that the Schottky barrier heights are about 0.67 eV by I-V and 0.68 eV by internal photoemission measurements. The Schottky barrier height was found to be constant for contacting to n-type GaAs in the temperature range between 150 and 300 K. From this fact, we conclude that the metal Fermi level is pinned relatively to the GaAs conduction band minimum in this case. This finding is similar to other epitaxial contacting cases, CoSi2/Si and ErSi2/Si, where the Fermi level pins to the nearest semiconductor band [J. Y. Duboz, P. A. Badoz, F. Arnaud d'Avitaya, and E. Rosenche, Phys. Rev. B 40, 10 607 (1989)].
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  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3199-3201 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Intersubband transitions in modulation doped, arbitrary potential profile quantum-well structures under an applied field are analyzed by solving the Schrödinger and Poisson equations self-consistently. This analysis is applied to the local-to-global transitions of a step well structure. The results show that although the band-bending effect is significant (∼25 meV) at a relatively high carrier density of 5.6×1011 /cm2 (∼3×1017 /cm3 ), the transition energies and absorption coefficients remain close to the flat band cases. This calculation confirms that the local-to-global transitions have large linear Stark shift and oscillator strength even at high doping.
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  • 16
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2304-2306 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report here the design, fabrication, and testing of an integrated thermocouple gauge. The gauge uses a thin-film Cr heater and a thin-film Cu–Cr differential thermocouple on a 5-×3-mm glass substrate. The thermocouple measures the difference between the heater and the substrate temperature. Calibration of the thin-film Cu–Cr thermocouple gauge was done by using a standard K-type thermocouple as reference. At a constant difference temperature the measured power input to the heater is a function of the surrounding vapor pressure. The thermocouple gauge was calibrated using a McLeod gauge with He, Ar, N2, H2O, and CO2 gases. Our measurements show that the range of the gauge can possibly be extended to the μTorr range. This gauge uses a standard thin-film processing technique for fabrication resulting in a lower cost of production. Also, small size makes this gauge versatile and unique in comparison to many commercial gauges.
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 35 (1994), S. 6270-6290 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: As a function of the coupling constant, it is shown that the Schwinger–Dyson equation has many bifurcation solutions that branch off from the trivial solution. Three of these solutions are obtained explicitly, using the parameter imbedding method and the Liaponov–Schmidt method. Application of these methods to other nonlinear problems is discussed. © 1994 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 35 (1994), S. 6693-6702 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The parameter imbedding method for the Fredholm equation converts it into an initial value problem in its parameter λ. The method is established for general operator equations of the form [I+fˆ(λ)]ψ=φ. It is particularly useful for studying spontaneous symmetry breaking problems such as contained in the nonlinear Schwinger–Dyson equation. © 1994 American Institute of Physics.
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  • 19
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A prototype surface ionization source coupled with a fixed-geometry extraction electrode system was commissioned on the Isotope Separator Accelerator (ISAC) ion source test stand at TRIUMF. The suitability of the ion source and extraction system for use in the ISAC facility was determined by a series of emittance measurements of the extracted beams. The test stand optics were successfully commissioned using the prototype ion source; emittance measurements of the mass-separated beams demonstrated that second- and third-order beam aberrations (introduced by the magnetic dipole mass separation) could be corrected by the use of multipole electrostatic optics elements. An upper limit of the root-mean-square-energy spread (2 eV) was deduced from the emittance measurements. Emittance measurements were performed at beam energies of 10–50 keV, as well as for ion masses ranging from Li+ to Rb+, to demonstrate the feasibility of the prototype for a variety of beam energies and masses. © 1998 American Institute of Physics.
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  • 20
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have reported a 15 mA dc H− multicusp source at the sixth International Ion Source Conference in 1995 at Whistler. Since then, the H− beam has been further upgraded to 20 mA for 25 kV dc extraction. The D− beam output of the new cusp source has also been measured at 25 and 12.5 kV energies. An 8 mA D− peak current at 25 kV with 0.5 π mm mrad normalized 4 rms emittance has been obtained. Special attention was given to the effects of gas flow, pumping speed, and neutralization on the 12.5 kV operation which is used for the D− injection into a 15 MeV D− cyclotron. At present, we are making an effort to test the effect of injecting Cs in the vicinity of the plasma aperture. On the other hand, a hybrid of filament plus LaB6 cathode mechanism has been tested for filament lifetime issue. The results from these tests are reported. In particular, the experience in operating this new source for the Triumf/Nordion TR30 cyclotron is summarized. © 1998 American Institute of Physics.
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