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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system has been developed to provide accurate calibration of electron detectors measuring in the energy range from approximately 10 eV to 50 keV. The principal component of the system is a large area (730 cm2), monoenergetic electron beam which is tunable in energy. This beam is produced by illuminating, in vacuum, a thin gold film deposited onto a quartz flat with ultraviolet light, such that photoelectrons are ejected from the gold surface. With the gold film floated at an adjustable negative voltage, the photoelectrons ejected from the surface are accelerated towards an electrically grounded screen which is positioned in front of the quartz flat. All high voltages in the beam system are guarded so as to eliminate any significant leakage current. The current leaving the gold surface which determines the beam intensity is measured using a specially designed picoammeter. Electron beam intensities of ∼106 electrons/cm2 s are produced by illuminating the gold photocathode with light from a 2-W mercury vapor lamp which has 90% of its output at 2537 A(ring). The resulting beam has an energy spread of 0.41 eV. Electron beam intensities of ∼107 electrons/cm2 s are produced with a 200 W medium pressure mercury arc lamp. For this case, the beam has a width in energy of 0.55 eV. Detectors to be calibrated are mounted within a set of computer-controlled rotational and translational tables. The tables allow the look direction of the detector to be oriented with respect to the beam in two orthogonal angles and two orthogonal directions. The entire calibration system operates within a set of Helmholtz coils that allow the Earth's magnetic field to be canceled. The voltage on the gold surface, the angular and spatial positioning of the detector, and the accumulation and display of the data are all controlled by a minicomputer.
    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: A space qualified 260° spherical plate electrostatic analyzer has been developed as a plasma diagnostic tool. The use of nested spheres and unusually shaped microchannel plates has resulted in a sensor capable of measuring simultaneously the three-dimensional populations of ions and electrons in a plasma. High-current microchannel plates and a new packaging of a hybrid preamplifier discriminator are combined with an uncommon high-voltage circuit. The combination of these features yields an analyzer that is compact and lightweight, efficient in its power consumption, and has a broad dynamic range.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2016-08-04
    Description: We are developing x-ray Thomson scattering for applications in implosion experiments at the National Ignition Facility. In particular we have designed and fielded MACS, a high-efficiency, gated x-ray spectrometer at 7.5–10 keV [T. Döppner et al. , Rev. Sci. Instrum. 85 , 11D617 (2014)]. Here we report on two new Bragg crystals based on Highly Oriented Pyrolytic Graphite (HOPG), a flat crystal and a dual-section cylindrically curved crystal. We have performed in situ calibration measurements using a brass foil target, and we used the flat HOPG crystal to measure Mo K-shell emission at 18 keV in 2nd order diffraction. Such high photon energy line emission will be required to penetrate and probe ultra-high-density plasmas or plasmas of mid-Z elements.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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