Fabrication of porous emitters for ionic liquid ion source by wire electrical discharge machining combined with electrochemical etching

Abstract

Ionic liquid ion source (ILIS) is a promising ion source, which can be applied to space propulsion, microfabrication, and surface modification. Fabrication of high-quality ILIS emitters is one of the key technologies for the application of ILIS. A new method is proposed for the fabrication of porous emitters with a designed shape. This method uses wire electrical discharge machining (WEDM) combined with electrochemical etching, and the porous emitter is fabricated by two steps. First, the porous metal is machined by WEDM to get the external geometry of the emitter. Then, electrochemical etching is employed to remove the recast layer. A series of experiments has been conducted to find the appropriate machining parameters. Experiments reveal that sharp porous emitter tips for the ILIS can be fabricated by WEDM combined with electrochemical etching at 5 V etching voltage. Moreover, the apex curvature radius of the emitter is controllable by adjusting the etching time. It is found that the apex curvature radius varies from 4.5 μm to 18.4 μm when increasing etching time from 40 s to 120 s at 5 V etching voltage. Those emitters have been applied to ILIS tests, and their I-V characteristics are investigated. Furthermore, this method has been used to machine dense fields of emitters. A 1 cm2 emitter array chip integrated with 676 emitters has been successfully machined, and the I-V characteristic curve of the emitter array chip is also achieved.