Plasma dynamics during the ignition transient period of an external discharge Hall thruster

The transient ignition process of Hall thrusters generates pulse current surges with amplitudes tens of times higher than the steady-state discharge current, posing significant challenges to power supply systems and electrode reliability. However, in conventional thrusters, direct observation of internal plasma dynamics is hindered by the obstruction of discharge channel walls, and existing particle-in-cell (PIC) simulation results lack experimental validation, leading to bottlenecks in elucidating the spatiotemporal evolution of plasma parameters and developing surge current suppression strategies. In this study, an open-structured external-discharge Hall thruster is employed to achieve direct visualization of plasma channel dynamics during ignition for the first time. By integrating high-speed ICCD imaging, PIC-Monte Carlo collision simulations, and transient circuit modeling, the regulatory mechanisms of anode voltage and propellant mass flow rate on plasma parameters and current surges are investigated. Experimental results demonstrate that increasing the anode voltage from 180 V to 240 V accelerates electron energy accumulation (up to 55 eV), elevates the pulse current peak from 1.49 A to 2.96 A, and reduces the ignition duration by 40%. When the propellant flow rate rises from 0.3 mg s−1 to 0.7 mg s−1, the neutral atom density increases to 1.8 × 1021 m−3, significantly enhancing ionization rates and driving the current peak to 3.68 A. Key phenomena, including dual-ionization-zone coordinated discharge and axial plume expansion, are experimentally validated. Furthermore, a dynamic plasma impedance model is established to propose staged voltage initiation and graded flow regulation strategies, which reduce the electrical stress factor from 10.84 to 2.27. These findings overcome the limitations of traditional diagnostic methods and model validation, providing theoretical insights and engineering guidelines for designing high-reliability Hall thrusters and optimizing power system redundancy.