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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Studies have been conducted to determine the feasibility of using the collisional cooling technique as a means of reducing energy spreads and emittances of sputter-generated negative-ion beams. A gas-filled rf-quadrupole ion cooler, equipped with provisions for decelerating ion beams to sufficiently low energies prior to cooling and reaccelerating them to high energies following the cooling process, has been designed and used to cool O− and F− ion beams with initial energy spreads, ΔE〉10 eV to final energy spreads, ΔE∼2 eV full width half-maximum. Overall transmission efficiencies of ∼14% for F− beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Direct extraction, negative-surface ionization, and sputter-type sources have been designed to efficiently ionize specific members of the group VII A elements (F, Cl, Br, I, and At) for use in the nuclear structure physics and nuclear astrophysics research programs at the Holifield Radioactive Ion Beam Facility (HRIBF). A negative surface ionization source that utilizes a solid, spherical geometry, LaB6 ionizer (φ≅2.7 eV) for negatively ionizing Cl, Br, l, and At. During off-line evaluation, the ionization efficiency for Cl− generation ranged between 15% and 20% and for Br− generation, between 15% and 25%. Chemically active elements, such as fluorine, are often released from refractory host materials in a variety of molecular forms. Consequently, the LaB6 surface ionization source, described above, is ineffective for simultaneously dissociating and negatively ionizing this element. To overcome this problem, a new concept source, referred to as the kinetic ejection negative ion source (KENIS), was developed. The source utilizes the Cs-sputter technique to effectively dissociate molecular carriers and ionize F at efficiencies in excess of 7%. The source has been used on-line to inject 〉3×107 17F−/s into the tandem accelerator and deliver ∼3×106 17F9+/s (fully stripped) to the research station for completion of important nuclear-astrophysics experiments. In this article, emphasis will be placed on the design details, materials of construction, ion optics, operational parameters, thermal transport properties, emittances, and measured ionization efficiencies for these sources. © 2002 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3668-3676 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed a slow, highly collimated, and bright sodium atom beam suitable for orientation and alignment studies in cold collisions. A combination of transverse-optical collimation, longitudinal cooling, rapid decoupling from the longitudinal cooling cycle, and a final "optical-force extrusion" stage produces an atom density of 1×1010 cm−3 within a beam-divergence solid angle of 2×10−6 sr. Rapid Zeeman-cooler decoupling results in a narrow laboratory velocity distribution of 5 m/s full width at half maximum and a cold binary intrabeam collision temperature of 4 mK. © 2000 American Institute of Physics.
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  • 4
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact, all-permanent-magnet, single-frequency electron cyclotron resonance (ECR) ion source with a large uniformly distributed ECR plasma volume has been designed and is presently under construction at the Oak Ridge National Laboratory. The central region of the field is designed to achieve a flat field (constant mod-B) which extends over the length of the central field region along the axis of symmetry and radially outward to form a uniformly distributed ECR plasma "volume." The magnetic field design strongly contrasts with those used in conventional ECR ion sources where the central field regions are approximately parabolic and the resulting ECR zones are "surfaces." The plasma confinement magnetic field mirror has a mirror ratio Bmax/BECR of slightly greater than 2. The source is designed to operate at a nominal rf frequency of 6 GHz. The central flat magnetic field region can be easily adjusted by mechanical means to tune the source to the resonant conditions within the limits of 5.5–6.8 GHz. The rf injection system is broadband to ensure excitation of transverse electric modes so that the rf power is largely concentrated in the resonant plasma volume which lies along and surrounds the axis of symmetry of the source. Because of the much larger ECR zone, the probability for absorption of microwave power is dramatically increased, thereby increasing the probability for acceleration of electrons, the electron temperature of the plasma, and, consequently, the "hot" electron population within the plasma volume of the source. The creation of an ECR "volume" rather than a "surface" is commensurate with higher charge states and higher beam intensities within a particular charge state. The source has also been designed so that it can be easily converted into a conventional magnetic field geometry source so that comparisons of the performances of the "volume" and "surface" forms of the source can be easily made. The design features of the source and rf injection system will be described in detail in this article. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1137-1141 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A modified feed-forward control system has been operated at the Brookhaven Accelerator Test Facility to control the phase and amplitude of two high power klystron rf systems used to power a photocathode rf gun and a traveling wave electron linac. The changes to the control algorithm include an improved handling of cross coupling between the amplitude and the phase channels, an improved calibration routine that allows for changes in the matrix elements due to the variable base-line and improved filtering. The modifications to the software include modularity, portability, and user-friendliness. Improvements to the hardware include a linearized phase and amplitude controller with dc biasing for an improved dynamic range. The feed-forward system can handle nonlinear and noninstantaneous systems. With simultaneous regulation of two channels, the phase and the amplitude fluctuations over a time span of more than 3 μS were reduced to less than ±0.2° and ±0.2%, from the initial ±2.7° and ±1.8%, respectively. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1661-1662 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Detector dead time in electron multiplier ion counting applications has been reduced. A first-in first-out buffer allows a traditional ion counting system to accept pulses 10 ns apart. Lower dead time (10 ns) results from elimination of electrical ringing that trails electron multiplier output pulses. The improved system has been tested on 34S/32S isotope ratio measurements.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1429-1432 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report a new type of normalization procedure for modulation spectroscopy experiments in order to obtain the relative change in the reflectance (transmittance) spectrum ΔR/R(ΔT/T). Our new technique utilizes a servomechanism driven variable neutral density filter which keeps the dc component of the signal from the detector constant by varying the intensity of the light striking the sample. This method is particularly useful for photoreflectance measurements which can have background problems due to scattered pump light and/or photoluminescence. Advantages for other modulation spectroscopies, particularly in the region of the fundamental band gap of semiconductors, also will be discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3992-3994 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocomposite CoPt:C films were investigated as potential media for extremely high-density recording. An annealing temperature of over 600 °C is necessary to form nanocomposite CoPt:C films consisting of C matrix and fct CoPt nanocrystallites with grain sizes of 8–20 nm and coercivities of 3–12 kOe. Coercivity and grain size increase with increasing annealing temperature and decreasing C concentration and they are insensitive to film thickness. The average activation volumes are about 0.9×10−18 cm3. The properties of these nanocomposite CoPt:C films can be tailored to satisfy the thermal stability, coercivity, and media noise requirements for extremely high-density recording. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1057-1059 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An optical laser trap with fluorescence excitation/emission capability has been integrated in a flow cytometric geometry for the study of microparticle confinement and off-axis fluorescence detection in laminar flow streams. Measurements of particle escape velocity, trapping efficiency, and fluorescence intensity are presented for 2 μm diameter dye-tagged latex microspheres in laminar flow streams having velocities of up to 12 mm/s. Experimental results are compared with theoretical values for flow velocity and fluorescence intensity and found to be in excellent agreement. © 1995 American Institute of Physics.
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the optical response of 700 nm optically thick Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high Tc superconductor films activated by a few mJ/cm2 laser pulses. We have systematically studied the dependence of optical response on temperature and laser intensity. Fast and slow components can be clearly identified. A 70 ps electric transient has been obtained when activated by a 3.3 mJ/cm2 laser at 80 K or by a 10 mJ/cm2 laser at 50 K. © 1995 American Institute of Physics.
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