Scanning optical pyrometer for measuring temperatures in hollow cathodes

Polk, James E.; Thornber, Ben; Dang, Lisa; Johnson, L. K.; Katz, Ira

doi:10.1063/1.2774828

Cited by 18 publications

(6 citation statements)

References 9 publications

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“…21 However, temperature decreases of this magnitude over a period of several hundred hours have been observed at the beginning of long duration tests. 24 The temperature decrease is generally attributed to long term conditioning of the emitter surface (removal of reactive contaminants and achieving a stable surface morphology and crystal structure) which results in a decrease in the work function.…”

Section: Comparison Of Experimental and Simulation Resultsmentioning

confidence: 99%

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Barium Depletion in Hollow Cathode Emitters

Polk¹,

Capece²,

Mikellides³

et al. 2009

45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Section: Comparison Of Experimental and Simulation Resultsmentioning

confidence: 99%

“…The temperature distribution measured along the axis of an emitter with the same geometry and operating conditions as the LDT cathode 21 was used in the simulations. The Ba partial pressure in the insert plasma near the emitter surface is calculated as part of the barium Ba solution.…”

mentioning

confidence: 99%

Barium Depletion in Hollow Cathode Emitters

Polk¹,

Capece²,

Mikellides³

et al. 2009

45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…Tests at JPL (for both cathode assemblies) will also be performed to measure the emitter temperature and the plasma properties inside the emitter region and along the cathode centerline. 46,47 These detailed internal cathode measurements will be used, in conjunction with simulations using the 2-D axisymmetric Orificed Cathode (OrCa2D) code, to obtain accurate estimates of cathode life. 48 , 49 An inner electromagnet test coil was fabricated, and instrumented with over 15 thermocouples.…”

Section: Component Testingmentioning

confidence: 99%

Overview of the Development of the Solar Electric Propulsion Technology Demonstration Mission 12.5-kW Hall Thruster

Kamhawi

Huang²,

Haag³

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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NASA is developing mission concepts for a solar electric propulsion technology demonstration mission. A number of mission concepts are being evaluated including ambitious missions to near Earth objects. The demonstration of a high-power solar electric propulsion capability is one of the objectives of the candidate missions under consideration. In support of NASA's exploration goals, a number of projects are developing extensible technologies to support NASA's near and long term mission needs. Specifically, the Space Technology Mission Directorate Solar Electric Propulsion Technology Demonstration Mission project is funding the development of a 12.5-kW magnetically shielded Hall thruster system to support future NASA missions. This paper presents the design attributes of the thruster that was collaboratively developed by the NASA Glenn Research Center and the Jet Propulsion Laboratory. The paper provides an overview of the magnetic, plasma, thermal, and structural modeling activities that were carried out in support of the thruster design. The paper also summarizes the results of the functional tests that have been carried out to date. The planned thruster performance, plasma diagnostics (internal and in the plume), thermal, wear, and mechanical tests are outlined. AbbreviationsAFRL = Air Force Research Laboratory ARRM = Asteroid Retrieval and Redirect Mission GRC = Glenn Research Center HEFT = Human Exploration Framework Team HEOMD = Human Exploration and Operations Mission Directorate JPL = Jet Propulsion Laboratory MS = Magnetically Shielded

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“…[14,15], were conducted in a vacuum facility at a base pressure of 10 −6 Torr. The cathode is of the standard configuration shown in the drawing in Propellant-grade xenon (99.9995% purity) was injected through the hollow cathode.…”

Section: Methodsmentioning

confidence: 99%

Materials characterization of impregnated W and W–Ir cathodes after oxygen poisoning

Polk

Capece

2015

Applied Surface Science

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A c c e p t e d M a n u s c r i p t Highlights: Hollow cathodes with impregnated tungsten and tungsten-iridium emitters were operated with 100 ppm of oxygen in the xenon gas flow for 480 and 80 hours, respectively.  Chemical and morphological changes were studied using scanning electron microscopy, energy dispersive spectroscopy, and laser profilometry.  High concentrations of oxygen accelerate the formation of tungstate layers in both types of emitters.  Deposits of pure tungsten were observed on the W-Ir emitter, indicating that tungsten is preferentially removed from the and transported in the insert plasma.  The W-Ir emitter exhibited less erosion and redeposition at the upstream end than the pure W emitter surface.Page 2 of 8 A c c e p t e d M a n u s c r i p t AbstractElectric thrusters use hollow cathodes as the electron source for generating the plasma discharge and for beam neutralization. These cathodes contain porous tungsten emitters impregnated with BaO material to achieve a lower surface work function and are operated with xenon propellant. Oxygen contaminants in the xenon plasma can poison the emitter surface, resulting in a higher work function and increased operating temperature. This could lead directly to cathode failure by preventing discharge ignition or could accelerate evaporation of the BaO material. Exposures over hundreds of hours to very high levels of oxygen can result in increased temperatures, oxidation of the tungsten substrate, and the formation of surface layers of barium tungstates. In this work, we present results of a cathode test in which impregnated tungsten and tungsten-iridium emitters were operated with 100 ppm of oxygen in the xenon plasma for several hundred hours. The chemical and morphological changes were studied using scanning electron microscopy, energy dispersive spectroscopy, and laser profilometry. The results provide strong evidence that high concentrations of oxygen accelerate the formation of tungstate layers in both types of emitters, a phenomenon not inherent to normal cathode operation. Deposits of pure tungsten were observed on the W-Ir emitter, indicating that tungsten is preferentially removed from the surface and transported in the insert plasma. A W-Ir cathode surface will therefore evolve to a pure W composition, eliminating the work function benefit of W-Ir. However, the W-Ir emitter exhibited less erosion and redeposition at the upstream end than the pure W emitter.

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Scanning optical pyrometer for measuring temperatures in hollow cathodes

Cited by 18 publications

References 9 publications

Barium Depletion in Hollow Cathode Emitters

Barium Depletion in Hollow Cathode Emitters

Overview of the Development of the Solar Electric Propulsion Technology Demonstration Mission 12.5-kW Hall Thruster

Materials characterization of impregnated W and W–Ir cathodes after oxygen poisoning

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