Microfabrication of capillary electrospray emitters and ToF characterization of the emitted beam

Dandavino, Simon, Ataman, C, Shea, H., Ryan, Charles and Stark, J. (2011) Microfabrication of capillary electrospray emitters and ToF characterization of the emitted beam. 32nd International Electric Propulsion Conference, Wiesbaden, Wiesbaden, Germany. 11 - 15 Sep 2011. (In Press)

Abstract

Microfabrication, assembly, and characterization of internally fed arrays of
electrospray emitters for spacecraft propulsion are discussed. Several different emitter geometries were fabricated, and the sprayed beams from these emitters are characterized for their ion/droplet composition. It is shown that with smaller inner diameters, ionic mode of operation can be achieved more easily, due to the increase in the hydraulic impedance. Up to 2000 sIsp was measured from capillaries with 5μm inner diameter and 100μm with 750V extraction voltage
using EMI-BF4. Due to the small dimensions of the microfabricated
capillaries, the onset and ionic mode operation voltages can be significantly lower than macroscopic emitters. The major failure mode for the emitters was the liquid overflow from the capillary tip, which can be resolved
through coatings that wet the ionic liquids differently. A detailed study of the wetting behavior of two ionic liquids is also presented for various
materials compatible with silicon microfabrication technology

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