Oscillations of iodine LaB₆ hollow cathode

Iodine-fed electric propulsion systems have achieved significant technological progress in recent years, the operating range of these systems remains fundamentally limited by ampere level iodine compatible hollow cathode technology. Preliminary studies on discharge characteristics have found that LaB₆ hollow cathode is a potential strategy. In this study, a conventional LaB₆ hollow cathode made with iodine-resistant materials was designed and tested in an iodine-compatible vacuum facility. The waveform, bispectral characteristics, and dispersion relation of the iodine hollow cathode were obtained and compared with the estimated collision reaction frequency. We analyzed the potential reaction processes both inside and outside the cathode and assessed how oscillation affects the lifetime of the iodine hollow cathode. The results indicate that the chaotic low-frequency oscillations were the main oscillation mode affecting the performance of the iodine cathode, involving multiple reaction processes that interfere with each other. The oscillation inside the cathode was mainly affected by vibrational excitation and iodine molecular ionization, while the oscillation outside the cathode was affected primarily by processes such as neutral gas flow, excitation, ionization, dissociation, and ion transit-time instability. The overall oscillation of iodine cathode is a non-dominant unstable mode with uniform energy distribution. A single 27-h self-sustaining experiment found that low-frequency oscillation has a significant impact on the emitter and the orifice, thereby reducing the cathode lifetime. The main reaction process inside and outside the iodine cathode and the influence relationship between the reactions were understood by the oscillation characteristics. It provides a theoretical basis to improve the performance of the iodine hollow cathode in the future.