Review of experimental diagnosis and numerical simulation of hollow cathode ion acoustic oscillations

Vollständiger Abstract

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Abstract Hollow cathodes are indispensable electron sources in electric propulsion systems, and their operational stability and lifetime are strongly influenced by plume discharge instabilities and energetic-ion bombardment. Under ion-acoustic-wave-induced unstable operating conditions, enhanced plasma oscillations can lead to excessive emitter erosion, increased plume noise, distorted ion energy distributions, and severe sputtering of the keeper and orifice, thereby degrading thrust stability and limiting the service life of electric thrusters. Although extensive experimental and numerical studies have been conducted, the physical mechanisms linking ion acoustic turbulence, discharge instability, anomalous electron transport, and energetic-ion generation remain incompletely understood. This review systematically summarizes recent advances in experimental diagnostics and numerical simulations of hollow cathode plume instabilities under ion-acoustic oscillations. Experimental diagnostic techniques, including emissive probes, ion saturation probes, high-speed imaging, Thomson scattering, retarding potential analyzer, electrostatic energy analyzer, and laser-induced fluorescence, are critically reviewed with emphasis on their measurement principles, applicability, advantages, limitations, and complementary capabilities. Furthermore, fluid, particle-in-cell (PIC), hybrid-PIC, and kinetic models are comparatively analyzed in terms of physical assumptions, applicable plasma regimes, predictive accuracy, and agreement with experimental observations. Particular attention is devoted to the treatment of anomalous collisions and wave–particle interactions responsible for energetic-ion acceleration. Beyond summarizing previous studies, this review identifies common bottlenecks in experimental diagnostics and numerical simulations, analyzes the physical origins of discrepancies across numerical approaches, and discusses future research priorities, including synchronized non-invasive diagnostics, multiscale self-consistent simulations, and lifetime-oriented hollow cathode design. A unified framework linking ion acoustic turbulence, discharge instability, energetic-ion generation, and cathode erosion is established, guiding the development of next-generation long-life electric propulsion systems.