The electrical breakdown of ${\mathrm{SF}}_6$ in the presence of floating metal particles is facilitated by two key factors: the role of floating metal particles and the nonlinear breakdown behavior of high-pressure ${\mathrm{SF}}_6$. However, the microscopic transient processes remain unclear, motivating this paper. Using two-dimensional fluid models, we investigate ${\mathrm{SF}}_6$ streamer breakdown induced by a floating linear metal particle under negative applied voltage. First, we identify a characteristic double-end streamer inception in the combined gap. Then, we propose the following-streamer (FS) mechanism to explain the metal particle’s role. Two following streamers, FS1 and FS2, arise from the interaction between space charge and metal particle. FS1 facilitates breakdown via the negative space-charge field generated by its head. FS2 facilitates breakdown by merging with FS1, accelerating its propagation and enhancing the electric field at the primary streamer head. Finally, we propose the side-streamer (SS) mechanism to explain the nonlinear breakdown behavior of high-pressure ${\mathrm{SF}}_6$. The SS is identified as a new forward ionization wave that develops along the sides of the primary streamer, due to photoionization-driven negative-ion accumulation. SS facilitates breakdown by merging with the primary streamer, increasing negative space charge and leading to three distinct propagation modes. Higher pressure increases the production rate of negative ions along the streamer sides, making SS more likely to form. Under overvoltage, the facilitating effect of SS diminishes as the background field $(E/N{)}_b$ strengthens, disappearing when $(E/N{)}_b$ exceeds 245 Td. This study provides new insights into the ${\mathrm{SF}}_6$ streamer breakdown mechanisms induced by floating metal particles and offers theoretical references for further investigation on the quantitative characterization.

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• Dielectric properties
• Nonlinear phenomena in plasmas
• Plasma discharges
• Plasma interactions
• Dusty or complex plasma
• Metals
• Nanoparticles
• Photoionization