Liquid flow induced by ion evaporation in an electrified meniscus.
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.
Higuera
F J
FJ
E. T. S. Ingenieros Aeronáuticos, Plaza Cardenal Cisneros 3, 28040 Madrid, Spain.