Beam Distribution Characteristics of a 30-cm Multimode Ion Thruster

To meet the design requirements of ion thrusters for China’s asteroid exploration mission, a beam distribution characterization platform was established. This study systematically investigates the ion current spatial distribution, beam divergence, and roll torque through integrated experimental and theoretical analyses. The results demonstrate that thrust density increases with both screen grid voltage and anode flow rate. As the anode flow rate increased from 0.986 to 2.036 mg/s, the peak current density measured by the probe rose from 0.224 to 0.398 mA/cm2. The spatial distribution of the ion beam, initially uniform, degraded beyond a critical operating point. The beam divergence angle exhibited a strong dependence on the net-to-total acceleration voltage ratio, decreasing continuously from 30.91° to 27.32° as the ratio increased from 0.72 to 0.88, beyond which it stabilized. Furthermore, the divergence angle demonstrated a clear minimum with respect to perveance, increasing beyond a critical value of$2.14\times 10^{-5}$$\mathrm{A/V}^{\wedge }$(3/2). Roll torque was found to scale nearly linearly with thrust, reaching a maximum of$221~\mu $N$\cdot $m. Crucially, this study identifies and quantifies that precise grid alignment is an effective method for suppressing roll torque. The findings provide critical insights and a foundational database for optimizing the design, control strategy, and on-orbit application of multimode ion thrusters, directly supporting upcoming deep-space missions.