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  • 1
    Electronic Resource
    Electronic Resource
    High current, low pressure plasma cathode electron gun (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 388-398 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A plasma-cathode electron gun based on a moderate pressure (〉5 mTorr) cold-cathode discharge and a high perveance, multiaperture accelerator was previously developed at Hughes Research Laboratories and produced electron beam currents of up to 1 kA at voltages of over 200 kV for pulse lengths of 100 μs. This gun was limited in pulse repetition frequency and duty by the gas-puff system that provided adequate gas pressure in the hollow cathode to operate the glow discharge while keeping the pressure in the beam transport region sufficiently low. We describe a new plasma cathode electron gun (PCE gun) that eliminates this problem by replacing the glow-discharge plasma generator in the electron gun by a low-pressure thermionic discharge in a magnetic multipole confinement chamber. Proper design of the plasma generator and electrical circuit provides high electron-current densities to the accelerator structure at very low gas pressure (〈10−4 Torr). The static gas pressure permits the pulse repetition frequency to be very high (〉1.5 kHz demonstrated) with electron beam currents up to 200 A at voltages up to 120 kV demonstrated. The design and performance of the PCE gun, along with several models used to predict and scale the performance, are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150212
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    Paper (German National Licenses)
    Fulltext
  • 2
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    High current, low pressure plasma cathode electron gun (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-02-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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    PAPER CURRENT
  • 3
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    Hollow Cathode and Keeper-region Plasma Measurements Using Ultra-fast Miniature Scanning Probes (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In order to support the development of comprehensive performance and life models for future deep space missions that will utilize ion thrusters, we have undertaken a study of the plasma structure in hollow cathodes using an new pneumatic scanning probe diagnostic. This device is designed to insert a miniature probe directly into the hollow cathode orifice from either the upstream insert region in the interior of the hollow cathode, or from the downstream keeper-plasma region at the exit of the hollow cathode, to provide complete axial profiles of the discharge plasma parameters. Previous attempts to diagnose this region with probes was Limited by the melting of small probes in the intense discharge near the orifice, or caused significant perturbation of the plasma by probes large enough to survive. Our new probe is extremely compact, and when configured as a single Langmuir probe, the ceramic tube insulator is only 0.5mm in diameter and the current collecting conductor has a total area of 0.002 cm2. A series of current-voltage characteristics are obtained by applying a rapid sawtooth voltage waveform to the probe as it is scanned by the pneumatic actuator into and out of the plasma region, The bellow-sealed pneumatic drive scans the probe 4 cm in the cathode insert region and 10 cm in the anode/keeper plasmas region at average speeds of about 1 mm/msec, and the residence time at the end of the insertion stroke in the densest part of the plasma near the orifice is measured to be only 10 msec. Since the voltage sweep time is fast compared to the motion of the probe, axial profiles of the plasma density, temperature and potential with reasonable spatial resolution are obtained. Measurements of the internal cathode pressures and the axial plasma-parameter profiles for a hollow cathode operating at discharge currents of up to 35 A in xenon will be presented.
    Keywords: Electronics and Electrical Engineering
    Type: 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Fort Lauderdale, Florida, July 11-14, 2004; Jul 11, 2004 - Jul 14, 2004; Fort Lauderdale, FL; United States
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    NASA TECHNICAL REPORTS
  • 4
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    Discharge Chamber Performance of the NEXIS Ion Thruster (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Nuclear-Electric Xenon Ion System (NEXIS) thruster was designed to produce greater than or equal to 70% efficiency at ISPs in excess of 6500 sec and total power levels in excess of 15 kW. In order to achieve this performance, the thruster requires a large area plasma generator capable of high propellant utilimtion efficiency and low discharge loss while producing a very flat, uniform beam profile. Fortunately, larger thrusters can be made more uniform and efficient due to the higher volume to surface ratio, provided that the magnetic cusp confinement is designed properly and the thruster length to diameter ratio is adequate. This paper describes the discharge chamber performance of the NEXIS Laboratory Model (LM) thruster. The LM discharge chamber is 65 cm in diameter at the grid plane and uses 6 ring-cusps to provide magnetic confinement of the plasma. The thruster was tested with flat carbon-carbon composite grids with the hole pattern masked to 57 cm in diameter and a conventional Type-B "1/2" diameter hollow cathode. During the preliminary "discharge only" tests, the LM thruster demonstrated profile factors of 0.84 and a discharge loss of about 160 eV/ion at 25 V discharge voltage and over 90% propellant utilization efficiency in simulated beam extraction experiments at 3.9 A of beam current. Analysis of the data from these tests used the discharge-only model developed by Brophy. Subsequent beam extraction experiments validated the key variables used in the model to predict the performance from the discharge-only data, and demonstrated 3.9 A of beam current at over 90% propellant utilization efficiency with a flatness parameter of better than 0.8 and a discharge loss of about 185 eV/ion. The slightly higher discharge loss measured during beam extractions was found to be due to a lower screen transparency in the as-manufactured LM grid set. Plasma measurements with a scanning probe internal to the thruster near the screen grid showed plasma densities over l x 10(exp 11) per cubic centimeter and electron temperatures of 3.5 to 5.5 eV depending on the operation parameters. The performance of the NEXIS discharge chamber contributed to the over 78% thruster efficiency measured during beam extraction at 7500 sec ISP and 25 kW of power, and over 81% thruster efficiency measured at 8500 sec ISP.
    Keywords: Plasma Physics
    Type: 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 11, 2004 - Jul 14, 2004; Fort Lauderdale, FL; United States
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    NASA TECHNICAL REPORTS
  • 5
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    Model of a Hollow Cathode Insert Plasma (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A 2-D axisymmetric fluid model of the plasma in the insert region of a hollow cathode is presented. The level of sophistication included in the model is motivated in part by the need to determine quantitatively plasma fluxes to the emitter surface. The ultimate goal is to assess whether plasma effects can degrade the life of impregnated inserts beyond those documented throughout the 30-50 year history of vacuum cathode technologies. Results from simulations of a 1.2-cm diameter cathode operating at a discharge current of 25 A, and a gas flow rate of 5 sccm, suggest that approximately 10 A of electron current, and 3.5 A of ion current return to the emitter surface. The total emitted electron current computed by the model is about 35 A. Comparisons with plasma measurements suggest that anomalous heating of the plasma due to two-stream instabilities is possible near the orifice region. Solution to the heavy species energy equation, with classical transport and no viscous effects, predicts heavy species temperatures as high as 2640 K.
    Keywords: Electronics and Electrical Engineering
    Type: 2004 Joint Propulsion Conference; Jul 12, 2006 - Jul 14, 2006; Fort Lauderdale, FL; United States
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    NASA TECHNICAL REPORTS
  • 6
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    Model of the Plasma Potential Distribution in the Plume of a Hollow Cathode (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In this paper we present results from a new model of the plasma potentials in the plume just downstream of the hollow cathode keeper. We examine the electron drift velocity as the hollow cathode plasma and neutral gas expand downstream of the keeper. If the drift velocity exceeds the thermal velocity a double layer potential structure develops that is the source of hot electrons. Ions are accelerated upstream through the double layer. The locations of the double layers are calculated using a simple model. It is shown that as the cathode gas flow increases, the location of the double layer moves farther downstream.
    Keywords: Plasma Physics
    Type: Joint Propulsion Conference; Jul 12, 2006 - Jul 14, 2006; Fort Lauderdale, FL; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Plasma generation near an Ion thruster disharge chamber hollow cathode (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In gridded electrostatic thrusters, ions are produced by electron bombardment in the discharge chamber. In most of these thrusters, a single, centrally located hollow cathode supplies the ionizing electrons. An applied magnetic field in the discharge chamber restricts the electrons leaving the hollow cathode to a very narrow channel. In this channel, the high electron current density ionizes both propellant gas flowing from the hollow cathode, and other neutrals from the main propellant flow from the plenum. The processes that occur just past the hollow cathode exit are very important. In recent engine tests, several cases of discharge cathode orifice place and keeper erosion have been reported. In this paper we present results from a new 1-D, variable area model of the plasma processes in the magnetized channel just downstream of the hollow cathode keeper. The model predicts plasma densities, and temperatures consistent with those reported in the literature for the NSTAR engine, and preliminary results from the model show a potential maximum just downstream of the cathode.
    Keywords: Spacecraft Propulsion and Power
    Type: 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 20, 2003 - Jul 23, 2003; Huntsville, AL; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Breakdown characteristics and conditioning of carbon and refractory metal electrodes (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: High voltage carbon and refractory metal electrodes employed in devices used in space, such as ion thrusters and traveling wave tubes, can be easily damaged by electrical breakdown and arcing events. Modification of the electrode surfaces due to these events can impact the voltage hold off capability of the surfaces, which could lead to additional arcing, further damage, and the potential for device failure. On the cathode-potential surface, the arc energy is deposited by all of the processes at the surface ultimately responsible for net electron emission, such as melting, vapor and particulate formation, sputtering, ion bombardment, etc. On the anode-potential surface, the energy is deposited from the plasma or electron stream that crosses the gap, which causes surface damage by local heating. In spite of this energy dependence on the damage, many systems that use arc discharges characterize the amount of material removed from the surfaces and the lifetime of the device for voltage hold-off by the amount of current that passes through the arc, or the 'Coulomb-rating'. The results of a series of tests that were preformed on the boltage hold off capability and damage to carbon-carbon composite surfaces and molybdenum surfaces due to induced arcing will be presented and discussed. Damage to the surfaces was characterized by the field emission performance after the arc initiation and SEM photographs for the different energy and coulomb-transfer arc conditions. Both conditioning and damage to the surfaces were observed, and will be related to the characteristics of the electrical breakdown.
    Type: IEEE Power Modulator Conference/High Voltage Workshop; May 24, 2004 - May 26, 2004; San Francisco, CA; United States
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    NASA TECHNICAL REPORTS
  • 9
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    Development and testing of carbon-based ion optics for 30-cm ion thrusters (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Carbon-based ion optics have the potential to significantly increase the lifetime of state-of-the-art ion thrusters which use molybdenum optics because of the lower sputter yield and greater packing density of the carbon materials.
    Keywords: Optics
    Type: 39th Joint Propulsion Conference; Jul 20, 2003 - Jul 23, 2003; Huntsville, AL; United States
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    NASA TECHNICAL REPORTS
  • 10
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    Extending hollow cathode life for electric propulsion in long-term missions (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper will present our understanding of the hollow cathode barium depletion mechanism and the design required to achieve the required life.
    Keywords: Spacecraft Propulsion and Power
    Type: AIAA Space 2004; Sep 28, 2004 - Sep 30, 2004; San Diego, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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