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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7094-7100 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory is presented to explain the observed electron emission characteristics of a hollow-cathode-based plasma source. The theory is compared with measurements made in a laboratory vacuum facility and is used to predict emission characteristics when the source plasma expands into an ambient space plasma. Crucial to understanding the observed emission current-voltage characteristic of hollow-cathode-type devices is the recognition of the role of emission current, not just the current in the main discharge circuit, in ionization of the neutral gas flowing through the device. This ionization can lead to breakdown of the sort that is familiar in many gas discharge devices. Equally crucial to understanding the low impedance capability of the device in coupling spacecraft to an ambient space plasma is recognition of the role of escaping as well as trapped source electrons in the formation of the space potential profile. The presence of these electrons, according to the theory, results in space electron emission current-voltage characteristics which are well approximated by those observed in laboratory chambers.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1993-12-15
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 3
    Publication Date: 1996-02-01
    Print ISSN: 0257-8972
    Electronic ISSN: 1879-3347
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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  • 4
    Publication Date: 2019-07-13
    Description: A report describing the operating principles of hollow-cathode-based plasma contactors emitting or collecting electrons from an ambient plasma is summarized. Preliminary experiments conducted to determine the noise generated by these plasma contactors in the emission-current return line and in the plasma near it are described. These noise data are measured as current fluctuations in the return line and to the Langmuir probe and then analyzed using a fast Fourier transform technique. The spectral compositions of the data are characterized using power spectral density plots which are examined to identify possible noise source(s) and production mechanism(s). The precautions taken in the construction and calibration of the instrumentation to assure adequate frequency response are described. Experimental results show that line-current noise levels are typically 2 percent of the electron current being emitted or collected. However, noise levels increase to as much as 20 percent of the electron current at a few electron-collection operating conditions. The frequencies associated with most of the noise were harmonics of the 60 Hz input to system power supplies. Plasma noise had characteristics similar in magnitude and frequency to those for the return-line noise, but they contained additional features at frequencies considered to be related to ion-acoustic instabilities. Also discussed is a new probe positioning system built to facilitate future plasma-contractor research.
    Keywords: PLASMA PHYSICS
    Type: NASA-CR-189140 , NAS 1.26:189140
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: An investigation conducted on the electrical interference induced by the operation of a hollow-cathode plasma contractor in a ground-based facility is described. The types of electrical interference, or noise, which are important to Space Station Freedom designers are classified as either conducted or radiated emissions. The procedures required to perform conducted and radiated emission measurements on a plasma contactor are examined. The experimental data obtained are typically examined in the frequency domain (i.e. amplitudes of the noise fluctuations versus frequency). Results presented indicate the conducted emissions, which are the current fluctuations from the contactor into the space station wiring, are affected by operating parameters such as expellant flow rate and discharge current. The radiated emissions, which are the electromagnetic waves induced and emitted by the contactor, appear to be influenced by the contactor emission current. Other experimental results suggest possible sources which are responsible for the observed noise. For example, the influence of the plasma environment downstream from the contactor on noise emission levels is described. In addition, a brief discussion is given on the correlation between conducted and radiated emissions and the mechanisms through which both are influenced by the plasma downstream of the contactor.
    Keywords: PLASMA PHYSICS
    Type: NASA-CR-191172 , NAS 1.26:191172
    Format: application/pdf
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  • 6
    Publication Date: 2019-07-13
    Description: Results of tests characterizing an 8-cm diameter ion source are presented. The tests were conducted in three separate vacuum test facilities at the University of Alabama-Huntsville, Colorado State University, and L3 Communications' ETI division. Standard ion optics tests describing electron backstreaming and total-voltage-limited impingement current behavior as a function of beam current were used as guidelines for selecting operating conditions where more detailed ion beam measurements were performed. The ion beam was profiled using an in-vacuum actuating probe system to determine the total ion current density and the ion charge state distribution variation across the face of the ion source. Both current density and ExB probes were utilized. The ion current density data were used to obtain integrated beam current, beam flatness parameters, and general beam profile shapes. The ExB probe data were used to determine the ratio of doubly to singly charged ion current. The ion beam profile tests were performed at over six different operating points that spanned the expected operating range of the DAWN thrusters being developed at L3. The characterization tests described herein reveal that the 8-cm ion source is suitable for use in (a) validating plasma diagnostic equipment, (b) xenon ion sputtering and etching studies of spacecraft materials, (c) plasma physics research, and (d) the study of ion thruster optics at varying conditions.
    Keywords: Spacecraft Propulsion and Power
    Type: AlAA Paper 2005-3882 , AIAA 41st Joint Propulsion Conference and Exhibit; Jul 10, 2005 - Jul 14, 2005; Tucson, AZ; United States
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