Performance and oscillation characteristics in mode transitions of a low-power planar Hall thruster with krypton propellant

Planar Hall thruster (PHT), characterized by the removal of the discharge channel, offers promising prospects for miniaturization and extended lifetime of Hall thruster. While PHTs operating with xenon (Xe) have been extensively studied, krypton (Kr), owing to its higher natural abundance and lower cost, has emerged as an attractive alternative propellant, motivating further investigation of its discharge characteristics. This study firstly investigates the discharge behavior of a low-power PHT operating with Kr and Xe propellants. With Xe, both the anode current and plume structure evolve smoothly as the voltage increases, whereas the Kr-fed PHT exhibits a unique three-stage mode transition accompanied by abrupt current drops and significant plume structure changes. Near the transition points, propulsion performance decreases sharply. Faraday probe measurements reveal large variations in ion current density distribution across modes, and correlation analysis identifies propellant utilization efficiency as the key factor governing performance degradation—unlike in Xe-fed PHTs in prior researches, where divergence efficiency dominates. Such difference is attributed to Kr's higher ionization energy and smaller ionization cross section, making ionization behavior more sensitive to mode transitions. Moreover, two distinct ionization regions were identified through such mode transitions: annular and central, corresponding to modes I and III, while mode II involves both. Oscillation behavior also differs markedly, with mode II showing amplitudes an order of magnitude higher than those in modes I and III. Finally, a keeper-off cathode mode effectively suppressed the second mode transition and improved thrust at 400 V by 220%, enhancing high-voltage performance. This study provides support for the low-cost, large-scale deployment of PHTs in satellite constellations.