Extractor Grid Effects on Beam Characteristics of Dual-Stage Ion Thruster

High thrust density per thruster area is the most desired achievement in current ion thruster designs. Dual-stage ion thruster concept is introduced to improve the ion beam focusing capability of single-stage thrusters in order to maximize the achievable thrust density for a fixed thruster area. In this paper, a two-grid ion thruster is converted to a dual-stage one by adding an extractor grid. Then, improvement of ion beam divergence characteristic is numerically investigated through the parametric study of extractor grid's geometrical and operational variables by a hybrid-particle-in-cell method. The sensitivity analysis shows that the beam divergence angle is very sensitive to acceleration-to-extraction voltage difference ratio. The effect of acceleration-to-extraction grid gap ratio is also significant. The initial dual-stage model is modified based on this result. The minimum divergence angle for the modified model is about 3.38° resulting in 70% and 60% improvement against the minimum divergence angle of the two-grid single-stage and the initial dual-stage numerical models, respectively.