Destructive evaluation of a xenon hollow cathode after a 28,000 hour life test

Sarver-Verhey, Timothy R.

doi:10.2514/6.1998-3482

Cited by 30 publications

(21 citation statements)

References 8 publications

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“…4 an end of life criterion has been derived and the model has been tuned to predict a lifetime of 28,000 hours fitting the experimental evidence for this cathode.…”

Section: Discussionmentioning

confidence: 99%

“…The computed surface coverage relative to Ba 3 WO 6 and BaWO 4 As it can be noted in the figures above the low work function compounds depletion starts at the downstream end of the cathode and then slowly moves upstream. This is due to the fact that the sputtering desorption rate is proportional to ion density and plasma voltage and that these two parameters are maximum at the downstream end of the cathode.…”

Section: 000 Hours Cathode Simulationmentioning

confidence: 99%

“…16. The experimental value of the amplification factor can be calculated from the data published by Server-Verhey 4,5 and is reported in Fig. 17.…”

Section: End Of Life Criterion Developmentmentioning

confidence: 99%

“…They are used as electron sources and neutralizers inside ion thrusters and Hall's effect thrusters and in the next future probably as stand alone microthrusters 1, 2 therefore their lifetime and performance are key elements in all the application mentioned above. Hollow cathodes developed by NASA have to date demonstrated a lifetime of 30,000 hours in ground testing 3 and 1,600 hours in orbit, however due to the requirements of longer lifetimes for deep space mission a large amount of efforts has been spent in lifetesting, characterization and modelling of hollow cathodes to ultimately estimate their lifetime [3][4][5][6][7][8][9][10][11][12][13][14] . During normal operation of the cathode the work function of the emitter surface is lowered from the typical value of the emitter material (for tungsten φ = 4.5 eV) down to about 2 eV thanks to the evaporation of BaO from the emitter core and its subsequent deposition on the emitting surface resulting in the formation of low work function compounds.…”

Section: Introductionmentioning

confidence: 99%

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Hollow Cathode Life-Time Prediction from Low Work Function Surface Coverage Evolution

Coletti

Gabriel

2008

44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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In this paper a procedure to update the plasma parameters relatively to changes of the hollow cathode surface work function has been developed. This procedure has been validated with experimental results and then coupled with the deposition/desorption model already developed by the authors. The evolution of the surface of the cathode tested for 28,000 hours by Sarver-Verhey has been simulated and from the data obtained an end of life criterion has been developed. Then using this criterion the ELT NSTAR discharge cathode has been simulated for various throttle conditions deriving the lifetime at TH0 (200,000 h), TH8 (100,000 h) and TH15 (25,000 h). The lifetimes found are in agreement with the theoretical expectation. The lifetime of the ELT NSTAR cathode under the throttling conditions used during the Deep Space 1 Spare Ion Engine life test has been found to be in excess of 30,000 hours and in particular 100,000 or more if the cathode is run at TH8 or lower from 30,000 hours onward.

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“…4 an end of life criterion has been derived and the model has been tuned to predict a lifetime of 28,000 hours fitting the experimental evidence for this cathode.…”

Section: Discussionmentioning

confidence: 99%

Section: 000 Hours Cathode Simulationmentioning

confidence: 99%

“…16. The experimental value of the amplification factor can be calculated from the data published by Server-Verhey 4,5 and is reported in Fig. 17.…”

Section: End Of Life Criterion Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Hollow Cathode Life-Time Prediction from Low Work Function Surface Coverage Evolution

Coletti

Gabriel

2008

44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…For example, a higher operating temperature due to increased work function ac-A c c e p t e d M a n u s c r i p t celerates the evaporation of Ba from the surface and the reaction between the impregnant and the tungsten, leading 45 to more rapid depletion of the barium supply. The formation of solid barium tungstate layers has been observed on portions of the cathode emitter surface in several long duration tests [4,5,6]. BaWO 4 is a poor electron emitter and a stable product of the reaction between the impregnant 50 and the tungsten matrix [7], so it will not act as an electron source or provide Ba or BaO to replenish the adsorbates on the tungsten surfaces in the insert.…”

mentioning

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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Rockets, Ion Propulsion

Molitor

Beattie

2003

Encyclopedia of Space Science and Technology

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Electric propulsion, the propelling of space vehicles by streams of electrically charged and electrically accelerated particles, is one of the most exciting concepts of the space adventure. It represents a fascinating area of applied science and technology, and it also provides the only feasible means of exploring the farthest reaches of our solar system by economically transporting large manned expeditions and heavy payloads to neighboring planets and probing the solar system away from the ecliptic plane. The concept of the ion rocket engine (the most useful form of electric propulsion for space missions) has existed for some time. However, the concept had to remain of only academic interest until the advent of the space age, and, particularly, until generating large amounts of electric power in space became a physical possibility. When solar–electric power source technology was established, the latter requirements, of course, became fulfilled. In general, an electric propulsion system has a power plant that consists of an energy source and a means of converting this energy into electrical energy and a propulsion device that converts the electrical energy into directed kinetic energy of its propellant. The two major problem areas of electric propulsion are ( 1 ) the development of sources of electrical energy that are sufficiently lightweight and ( 2 ) the transfer of this energy to the propellant to provide high exhaust velocities efficiently. The first problem, along with the general need for power in space, has given strong impetus to fundamental and applied work in developing lightweight solar panels. These areas of research and development have been vital to the future of electric propulsion and obviously have impacted many other important satellite and spacecraft applications. A solution to the second problem, an efficient propulsion device, is the subject of this article. Generic types are discussed. The electron‐bombardment ion thruster is the most mature and the most tested and is a major focus of this article. A sampling of results from space missions are reviewed.

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Destructive evaluation of a xenon hollow cathode after a 28,000 hour life test

Cited by 30 publications

References 8 publications

Hollow Cathode Life-Time Prediction from Low Work Function Surface Coverage Evolution

Hollow Cathode Life-Time Prediction from Low Work Function Surface Coverage Evolution

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

Rockets, Ion Propulsion

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