Vacuum Surface Discharge Behavior and Evolution Characteristics of Fluorinated Polyimide under High-Frequency Electrical Stress

Under vacuum high-frequency electrical stress, polyimide (PI) films face severe surface discharge risks, which significantly affect their insulation stability in spacecraft dielectric systems. In this study, fluorinated polyimide (FPI) films with different fluorine contents were prepared, and a vacuum high-frequency surface discharge testing platform was established to systematically investigate their discharge characteristics. The results show that the introduction of fluorinated groups increases the surface electrical conductivity and thermal conductivity of the films. The discharge inception voltage increased from 1.88 kV for pure PI to 2.38 kV for 50% FPI, with a 26.6% increase. In addition, a non-equilibrium plasma model was constructed to dynamically simulate the formation process of discharge channels and the multiphysical evolution mechanisms. The results reveal that the front region of the discharge channel exhibits a coupled feature of “high density-low temperature-high reaction rate,” with significant electric field shielding and energy dissipation observed at the electron avalanche position. Fluorinated groups effectively suppress the establishment of surface discharge channels by reducing the secondary electron emission yield (SEEY) and dielectric constant, thereby weakening the electron multiplication effect and space charge accumulation. This study, from the perspectives of material regulation and physical mechanisms, provides theoretical support for optimizing the insulation performance of polyimide materials under vacuum high-frequency conditions.