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Emission measurements from planar arrays of porous ionic liquid ion sources

We present current emission measurements from arrays of 480 porous ionic liquid ion source emitters for applications in space propulsion and in the processing and analysis of materials. The emitters are fabricated with a top-down approach from 10 × 10 × 1 mm3 bulk porous nickel and are housed within a microetched silicon frame and stainless-steel aperture-matching extraction grids. Measurements of emitted and collected currents are reported using two ionic liquids (ILs), EMI-BF4 and EMI-Im. Total beam currents up to about 400 µA can be sustained through passive feeding with IL fed from the rear of the bulk porous substrate. These currents are in agreement with previous work where currents of about 1 µA were observed from single emitters. Ion transparencies as high as 0.95 are achieved with manually assembled grids. Current emission displays reasonable symmetry between polarities, although slight differences could yield to the accumulation of one type of ion in the source leading to electrochemical reactions despite voltage alternation. Strong current decays with time and evidence of surface contamination reinforce this hypothesis. Future work should address this issue through closed-loop control of charge emission.