Effect of first-stage anode axial position on discharge characteristics of a double-stage anode layer thruster

In a double-stage anode layer thruster, the additional first-stage anode modifies the plasma distribution and potential structure, making the discharge characteristics sensitive to its axial position. However, the effect of the first-stage anode axial position on the discharge characteristics remains insufficiently understood. In this study, Particle-in-Cell numerical simulations are combined with diagnostic experiments to investigate the influence of the first-stage anode axial position. Two quantitative parameters, namely the effective ionization rate and the relative ionization–acceleration decoupling degree, are introduced to characterize the spatial relationship between ionization and acceleration processes. The PIC simulation results show that, as the first-stage anode moves toward the channel exit: (1) the peak ionization rate along the mid-radius first increases by approximately 10% and then rapidly decreases to about 50% of its initial value. This trend is mainly related to the combined effects of the neutral gas number density distribution and magnetic field strength, with the role of neutral gas distribution becoming increasingly significant; (2) the relative ionization–acceleration decoupling degree and ion energy loss both decrease, accompanied by a reduction in current utilization efficiency. These results indicate that the change in the spatial overlap between the ionization region and the acceleration region is an important factor affecting the discharge performance. In addition, the discrepancies between the PIC predictions and Faraday-probe measurements are within 10%, and the PIC results show qualitative consistency with the OES-derived projected distributions, supporting the use of the numerical model for comparative trend analysis.