Electrohydrodynamic capillary source of ions and charged droplets

Krohn, V.E.

doi:10.1063/1.1663380

Cited by 39 publications

(16 citation statements)

References 14 publications

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“…All of the resultant droplet average specific charges, which were in the range from 0.1 to 1.0 C/kg, were found to be within an order of magnitude of their Rayleigh limit. This compares well in the subject droplet diameter range with the results of other investigators using similar systems and different, conducting liquids (Hendricks 1962, Krohn 1974, and Lue and Kelly 1987.…”

Section: Fig 2 Ehd Spray Coordinate Systemsupporting

confidence: 77%

Experiments characterizing the interaction between two sprays of electrically charged liquid droplets

Snarski

Dunn

1991

Experiments in Fluids

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Experiments were conducted to characterize the interaction between two sprays of electrically charged ethanol droplets. The micrometer-size droplet sprays were generated electrohydrodynamically by applying a high positive voltage to two adjacent parallel needles that were located above a distant, electrically grounded funnel. The resultant droplet axial and lateral velocity components and diameter were measured as a function of needle spacing and applied voltage using a Phase Doppler Particle Analyzer. Data were acquired at two axial positions below the needles' tips, for two needle spacings, four applied voltages and at a single flow rate.The results revealed that an increase in applied voltage yielded an increase in the spray charge density. This produced an increase in both the axial and lateral droplet velocity components and a decrease in the droplet Sauter mean diameter and in its variation across the spray. An increase in needle spacing yielded a decrease in the axial velocity component. The lateral velocity component and the Sauter mean diameter, however, were not noticeably affected by this increase. Photographic data established a relationship between the lateral half-width of the spray and axial distance. This was used to identify a nondimensional similarity between the axial mean velocity component and lateral position. The results collectively support that appropriate variations in the applied voltage and needle spacing can yield more spatially uniform mean velocity component and Sauter mean diameter profiles. These variations bring about increased mixing between the two needles' sprays and, thus, an enhanced development of the combined droplet spray.

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Section: Fig 2 Ehd Spray Coordinate Systemsupporting

confidence: 77%

Experiments characterizing the interaction between two sprays of electrically charged liquid droplets

Snarski

Dunn

1991

Experiments in Fluids

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“…The condition that these two contributions are of the same order, namely that ␥ ١ · n ϳ 1 2 ⑀ 0 E n 2 , where ␥ is the surface tension of the liquid and E n is the electric field normal to its surface, equal to E 0 at the evaporating cap, determines the characteristic curvature radius of the cap as R 0 = ␥ / ⑀ 0 E 0 2 (see Ref. [30]). The velocity of the liquid in the cap can be estimated from this R 0 and typical values of the total evaporation current I ϳ͑q / m͒R 0 2 , where is the density of the liquid.…”

Section: B Flow Of the Liquidmentioning

confidence: 99%

Liquid flow induced by ion evaporation in an electrified meniscus

Higuera

2004

Phys. Rev. E

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A simple model is proposed for the flow around the apex of a meniscus of a liquid undergoing ion evaporation in a vacuum under the action of a high electric field. The model includes a simplified description of the effect of the space charge surrounding the evaporating surface, and the idealizations that ion evaporation occurs at a constant surface field and that the electric field and viscous forces are negligible in the liquid. In agreement with known experimental and theoretical results for liquid metal ion sources, numerical solutions of the model problem show that the meniscus develops a protrusion and the current-voltage characteristic is linear in a range of voltages above an extinction voltage at which evaporation switches off. An oscillatory regime and transient evolutions ending in surface pinch-off and the emission of a drop are described, and the stabilizing effect of the pressure variations due to the evaporation flux is discussed. Asymptotic estimates for large evaporation flow rates are worked out.

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“…In 1973 Krohn [Krohn, 1974] reported an electrohydrodynamic (EHD) source and described its operation in terms of the Rayleigh limit on the field on a liquid drop and field evaporation. He concluded that an EHD source would emit ions from the tip of a cone with a finite end radius established by a balance of removal of material by field evaporation and fluid flow towards the apex.…”

Section: Ymentioning

confidence: 99%

“…Krohn also predicted that such an ion source would be of great utility since it would be able to emit significantly more ion current than a gas field ionization source. Shortly thereafter Krohn and Ringo [Krohn, 1974] reported a primitive scanning focused ion beam system using a capillary source of Ga. The system consisted of the LMIS, an einzellens, a stigmator-deflector system and a target with an electron multiplier for secondary electron detection.…”

Section: Ymentioning

confidence: 99%

“…While there would still be significant space-charge, the shielding effect of the body of the cone would be reduced. Such an idea had been proposed earlier by Krohn and Ringo [Krohn, 1974] as a way around the problem of the space charge they realized would be present, but they did not analyze it in any detail. Kang and Swanson used a computational method due to Kang [Kang, 1981] called "spherical coordinate with increasing mesh" (SCWIM), that made it possible to model the electric field due to a field emitter located near an electrode that had dimensions many order of magnitude large than the emitter.…”

Section: Physics Of Liquid Metal Ion Sourcesmentioning

confidence: 99%

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