Spatial uniformity of the current emitted by an array of passively fed electrospray porous emitters

Ionic liquid ion sources (ILIS) have a broad range of applications ranging from focused ion beams (FIB) to spacecraft propulsion. For space thrusters, having a beam of ions of high velocity and low energy spread results in high specific impulse (a measure of the efficiency of propellant consumption) and high power efficiency. For FIB applications, these traits benefit focusing and resolution respectively. Since typical current levels emitted by individual ILIS range from tens of nA to a few μA, both applications often require using arrays of emitters in order to increase the total beam current; i.e. the thrust level in the case of a thruster or the throughput in ion milling applications. So far, most studies of emitter arrays have dealt with experimental measurements of global, spatially-averaged, properties and theoretical analyses generally assume that all emitters operate in a similar manner, so that scaling of the current is linear with the number of emitters. In this work we use a current probe to explore the uniformity properties of the current emitted by an array of porous emitters. We present measurements of the current density of both the array and individual tips, and analyze the reason and implications of the experimental observations.