Study on the Plume Divergence Characteristics of a Triple-Grid Electrospray Thruster

The triple-grid electrospray thruster exhibits superior plume focusing performance. To clarify the effects of structural parameters on the plume divergence characteristics of triple-grid electrospray thrusters, the beam current distribution and plume divergence half-angle were experimentally measured using a planar current probe array. The influences of structural parameters, including the emitter–extractor gap and extractor slot width, on both plume divergence and thruster performance were analyzed. Experimental results indicate that grid structural parameters strongly affect plume divergence. Under the tested operating conditions, the plume divergence half angle ranges from 14.7° to 18.7° when the emitter–extractor gap increases from 200 μm to 500 μm, and from 15.8° to 19.3° when the extractor slot width increases from 400 μm to 1200 μm. The divergence half angle increases by approximately 0.3° per 100 μm increase in extractor slot width, while it decreases by approximately 0.9° per 100 μm increase in emitter–extractor gap. In comparison to a traditional single-grid thruster, the triple-grid arrangement decreases the divergence half-angle by roughly 50% overall. Furthermore, these structural parameters significantly influenced thruster performance. The onset voltage increased with larger gaps and wider slots. The maximum emission current rose with extractor slot width, but was insensitive to the emitter-extractor gap. Thrust and specific impulse are enhanced with larger emitter–extractor gap and extractor slot width, while the thrust-to-power ratio shows a slight decrease under the same variations.This study provides important insights for the optimized design of focused electrospray thrusters by quantitatively establishing the relationships between grid geometry, plume divergence, and performance.