Electrochemical discharge etching of porous tungsten emitters for field emission electric propulsion applications.

Field Emission Electric Propulsion (FEEP) systems offer high specific impulse and precise low thrust capability, making them suitable for micro propulsion applications. Porous tungsten is a promising material option for field emission emitters, offering advantages such as the formation of sharp tips and pore structures that enhance propellant transport through capillary action. However, the fabrication of well-defined porous tips remains insufficiently understood in terms of the relationship between etching process parameters and resulting structures. In this study, a spark-assisted electrochemical discharge etching was applied to fabricate porous tungsten emitter needles tailored for FEEP applications. Key process parameters, including applied voltage, power supply type, electrolyte type, molar concentration, and initial porosity, were investigated to establish an electrochemical etching domain. Distinct etching regimes associated with different morphological outcomes were identified, and the process window for forming viable porous emitter tips was found to be significantly constrained, with failure modes such as tip collapse, loss of porosity, and surface sealing observed outside this range. Under certain conditions, EDS analysis further revealed the formation of a multicomponent crust layer enriched in oxygen and potassium, which suppressed porosity preservation and influenced the resulting tip morphology. The fabricated emitter was integrated into a FEEP propulsion module, and preliminary field emission experiments conducted under vacuum conditions demonstrated emission feasibility.