This study investigates the low-frequency ionization instability, high-frequency ion acoustic turbulence, and the energy distributions of energetic ions in ampere-level hollow cathodes. The effects of discharge currents and gas flow rates on discharge instabilities and energetic ion distributions are systematically analyzed, focusing on the mechanisms of ion-acoustic waves at both low- and high-frequency. Key factors influencing the power-law ‘ η ’ ( ϕ 2 ∝ ω η , η < 0 ) of high-frequency ion acoustic waves are identified, including electron trapping, ion resonance broadening, and the nonlinear Landau damping effect. Furthermore, the generation mechanisms of energetic ions are illustrated at the micro (e.g. anomalous collision frequency ‘ ν an IAT ’ induced by IAT) and macro (e.g. discharge voltage) levels. Correlation analysis reveals the relationships between energetic ions, low-frequency ionization instabilities, and high-frequency ion acoustic turbulence. These findings offer valuable insight into the unstable discharge oscillations of ampere-level hollow cathodes and the generation of energetic ions. It provides guidance for optimizing the discharge parameters of hollow cathodes, thus improving the endurance and stability of the cathode.

The large difference in the working performance of a hollow cathode plasma contactor between the ground and actual on-orbit environments will cause difficulties in selecting a ground-test schemes to fully simulate the contactor real on-orbit characteristics. In this study, the effect of the simulated anode size and structure, the simulated anode surface state, the flow rate of background working gas, and the background plasma density on the emission characteristics and plume structure of the contactor are studied. Three self-made simulated anodes of different sizes and structures are applied in the ground experiments. The change of anode surface state (particularly the ability of absorbing electrons) is realized by dividing the self-made simulated anodes into four double-separated regions and alternatively electrically isolating them. An additional gas channel and an auxiliary contactor are used to create background working gas and a low-Earth-orbit plasma atmosphere, respectively. The voltage–current curves as well as the plasma parameter distributions at the contactor exit and in the far-field regions are determined under different regimes and working conditions. The relationship between the contactor’s emission characteristics and plume structure is clarified. The experimental results could provide useful information for instructing the contactor design and developing a real on-orbit experiment plan.