Dynamic Three-Wave Coupling between Local Sporadic Spokes and Emergence of Global Breathing Oscillation in Partially Magnetized Cross-Field Plasmas

Localized small-scale events can induce significant and unexpected large-scale effects in physical systems. Here, we apply this principle to partially magnetized plasmas, focusing on key unresolved wave-related phenomena that have hindered technological progress. Our study provides the first experimental evidence that intermittent three-wave coupling triggers a low-frequency breathing oscillation. This oscillation arises from nonlinear interactions between two coherent rotating spokes. A comprehensive analysis of frequency spectrograms derived from fast camera images and discharge current signals reveals interactions between rotating spokes with different mode numbers, driving the system into a nonlinear regime. Simultaneously, the global breathing oscillation becomes pronounced. An intriguing observation is the dynamic creation and annihilation of both small- and large-amplitude spokes within this regime. Notably, sporadic breathing oscillations are observed, characterized by globally reduced light emission as large-amplitude spokes grow. Finally, we demonstrate nonlinear coupling and energy transfer between the local sporadic spokes and the global breathing oscillation, suggesting that the oscillating azimuthal electric field serves as the energy source for additional ionization within the plasma. This intriguing coupling behavior between local and global events presents a challenge for developing theories and simulations, marking a significant step forward in designing partially magnetized source to optimize stability and confinement.