Characterization of Conical Ionic Liquid Ion Sources for 2-D Electrospray Thruster Arrays on Porous Substrates

Abstract

Emission data from a new geometry of Ionic Liquid Ion Sources using porous materials are presented. Ionic liquids are molten salts at room temperature which have near zero vapour pressure. When used in electrospray thrusters, these sources provide an efficient thrust mechanism and, due to their low vapor pressure, eliminate the need for complex propellant feed systems. By emitting pure ion beams rather than mixed ion/droplet emission, small high efficiency thrusters capable of providing specific impulse levels of several thousand seconds can be realized. The latest developments of these thrusters, using conical emitters micro-fabricated from porous substrates, are presented. Porous substrates provide liquid flow over a wide range of emitted currents, accommodating steady, stable emission of ion beams. Conical type emitters, fabricated on a planar porous substrate are well suited for high density 2-D arrays as they allow for both passive propellant feed through the bulk and simplified grid alignment compared with arrays formed from multiple emitter array substrates. This paper confirms that such conical emitters can provide beam currents of 100's of nA up to several μA with beams composed of pure ions with no charged droplets detected, as has previously been observed using alternative emitter geometries.