Initiation of Electrical Breakdown in Ultrahigh Vacuum

Alpert, D.; Lee, D. A.; Lyman, E. M.; Tomaschke, H. E.

doi:10.1116/1.1491722

Cited by 236 publications

(74 citation statements)

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“…19 as a function of grid spacing for the CC material. The trend of increasing enhancement factor with grid spacing follows the trend observed by others 8,[13][14][15] , however, one important difference is that most published work shows the enhancement factor leveling off between 1 and 2 mm grid spacing. This difference could be due to the fact that published work has focused on solid flat and solid spherical electrodes whereas we are using flat electrodes with holes.…”

Section: Enhanced Electric Field Evaluationmentioning

confidence: 50%

“…Thus at larger grid gaps, fringing effects may become more significant at influencing the overall enhancement factor while the microstructure at the accelerator grid surface most likely remains unchanged. Analysis reported by Alpert 13 using a model of a pair of semi-infinite slab electrodes with rounded corners, indicate that when the gap spacing becomes large compared to the radius of curvature at the edges of the electrodes, the enhancement factor β FE2 may become appreciable. The fact that the gridlets used in this study did not have rounded corners could also partially explain the lack of a saturation point in the enhancement factor at the largest grid gaps.…”

Section: Enhanced Electric Field Evaluationmentioning

confidence: 99%

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Electric Field Breakdown Properties of Materials Used in Ion Optics Systems

Martínez¹,

Williams²,

Goebel³

2006

42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Measurements are presented of the electric field at breakdown for perforated flat plates fabricated from carbon-carbon (CC) composite, Poco graphite, pyrolytic graphite (PG), and molybdenum. The perforated flat plates represent electrodes used in ion sources and ion thrusters and measurements are made with and without ion beamlet extraction through the perforations. A ranking of the materials is presented of their suitability in ion source applications in terms of their electrical breakdown characteristics. For effective use in space missions, materials for ion optics systems must be capable of withstanding moderate electric field stress for long periods of time. In this regard, a simple analysis is presented where thrust density is shown to vary with the square of the electric field. This result suggests that a 50% increase in electric field will result in 125% higher thrust density and a thruster area reduction factor of 0.44. The reduction in thruster area would enable a commiserate decrease in thruster and gimbal specific mass. Experimental data are presented on the field emission onset, electric field enhancement factor, and electrical breakdown properties of the materials listed above as a function of conditioning state, grid spacing, and charge transfer level per arc. Tests results are presented for both beginning of life electrodes and for electrodes that have been heavily worn.

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Section: Enhanced Electric Field Evaluationmentioning

confidence: 50%

Section: Enhanced Electric Field Evaluationmentioning

confidence: 99%

Electric Field Breakdown Properties of Materials Used in Ion Optics Systems

Martínez¹,

Williams²,

Goebel³

2006

42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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show abstract

“…Electron emission from sharp, well-cleaned tips follows closely to the Fowler-Nordheim field emission law and its later modifications taking into account finite temperature and other refinements (Alpert et al, 1964;Noer, 1982;Halbritter, 1983) and takes place typically at 1-2 GV/m surface field. (Since the dependence of the current density on the electric field E is proportional to E 2 exp(−1/E), the emission increases rapidly from insignificant to large values.)…”

Section: Electron Field Emission Currentmentioning

confidence: 99%

On the feasibility of a negative polarity electric sail

Janhunen

2009

Ann. Geophys.

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Abstract. An electric solar wind sail is a recently introduced propellantless space propulsion method whose technical development has also started. In its original version, the electric sail consists of a set of long, thin, centrifugally stretched and conducting tethers which are charged positively and kept in a high positive potential of 20 kV by an onboard electron gun. The positively charged tethers deflect solar wind protons, thus tapping momentum from the solar wind stream and producing thrust. Here we consider a variant of the idea with negatively charged tethers. The negative polarity electric sail seems to be more complex to implement than the positive polarity variant since it needs an ion gun instead of an electron gun as well as a more complex tether structure to keep the electron field emission current in check with the tether surface. However, since this first study of the negative polarity electric sail does not reveal any fundamental issues, more detailed studies would be warranted.

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“…The paper by Alpert and colleagues [1] has an excellent synopsis of the early research viewed from a mid 1960's perspective. Field emission from cathode micro-protrusions and accelerated loosely bound macro-particles explained much of the existing data obtained with small and large gaps, respectively.…”

Section: History Of Field Emission and High Voltage Breakdown Researchmentioning

confidence: 99%

“…This allowed a determination of the emission area and enhancement factor, β, for a single emission site if a work function was assumed. A work function value of ~ 4.5 eV applies to most electrode materials and gives typical enhancement factors of 100 or more over the theoretical value [1] of the E-field of ~ 6.5 x 10 9 V/m (6.5 x 10 4 kV/cm) for emission in a "perfect" vacuum gap. This model appeared to explain the field emission phenomenon until the presence of visible light and no obvious metallic protrusions were observed at the emission sites.…”

Section: History Of Field Emission and High Voltage Breakdown Researchmentioning

confidence: 99%

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

Stygar¹,

Savage²,

Ives³

et al. 2003

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This research consisted of testing surface treatment processes for stainless steel and aluminum for the purpose of suppressing electron emission over large surface areas to improve the pulsed high voltage hold-off capabilities of these metals. Improvements to hold-off would be beneficial to the operation of the vacuum-insulator grading rings and final self-magnetically insulated transmission line on the ZR-upgrade machine and other pulsed power applications such as flash radiograph and pulsed-microwave machines. The treatments tested for stainless steel include the Z-protocol (chemical polish, HVFF, and gold coating), pulsed E-beam surface treatments by IHCE, Russia, and chromium oxide coatings. Treatments for aluminum were anodized and polymer coatings. Breakdown thresholds also were measured for a range of surface finishes and gap distances. The study found that: 1.) Electrical conditioning and solvent cleaning in a filtered air environment each improve HV hold-off 30%. 2.) Anodized coatings on aluminum give a factor of two improvement in high voltage hold-off. However, anodized aluminum loses this improvement when the damage is severe. Chromium oxide coatings on stainless steel give a 40% and 20% improvement in hold-off before and after damage from many arcs. 3.) Bare aluminum gives similar hold-off for surface roughness, R a , ranging from 0.08 to 3.2 µm. 4.) The various EBEST surfaces tested give high voltage hold-off a factor of two better than typical machined and similar to R a = 0.05 µm polished stainless steel surfaces. 5.) For gaps > 2 mm the hold-off voltage increases as the square root of the gap for bare metal surfaces. This is inconsistent with the accepted model for metals that involves E-field induced electron emission from dielectric inclusions. Micro-particles accelerated across the gap during the voltage pulse give the observed voltage dependence. However the similarity in observed breakdown times for large and small gaps places a requirement that the particles be of molecular size. This makes accelerated micro-particle induced breakdown seem improbable also. 4

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Initiation of Electrical Breakdown in Ultrahigh Vacuum

Cited by 236 publications

References 0 publications

Electric Field Breakdown Properties of Materials Used in Ion Optics Systems

Electric Field Breakdown Properties of Materials Used in Ion Optics Systems

On the feasibility of a negative polarity electric sail

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

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