Development and Characterization of Electrochemically Machined Tungsten Extractor Electrodes for Electrospray Thrusters

Abstract

This work explores electrochemically machined (ECM) tungsten extractors as an alternative to microfabricated silicon, in order to benefit from manufacturability, improved ion optics through chamfered apertures, reduced secondary electron emission, and the potential for thinner geometries. A custom ECM fabrication process employing a linearly oscillating cathodic paddle in sodium hydroxide was designed to manufacture extractors and increase aperture uniformity. Using through-mask ECM, a 76.2 µm thick tungsten extractor was fabricated, achieving a mean aperture diameter of 368 µm with a standard deviation of 29 µm. The extractor was integrated with a modified version of the MIT ion electrospray propulsion system (iEPS) to form a complete thruster. Characterization included current-voltage sweeps, angular beam scans, and retarding potential analysis. Measured efficiencies are comparable to previous iEPS thrusters, with intercepted currents ranging approximately between 1–2% of emitted current. These results demonstrate that ECM tungsten extractors can deliver at least similar performance to existing designs while offering improved manufacturability and scalability for future electrospray propulsion systems.