The discharge mode of a multi-hollow dielectric barrier discharge (MHDBD) plays an important role in the treatment outcomes but has not been well studied. In this study, an MHDBD is fabricated to investigate the discharge characteristics and the mode transition from both electric and optical perspectives. Three discharge modes are recognized with the increase of the applied voltages: inner-wall discharge, mode A (12–13.3 kV); hole-inside discharge, mode B (13.4–14.3 kV); and hole-surface hybrid discharge, mode C (≥14.4 kV). It is found that the transferred charges and the produced reactive species increase slowly in mode A, then augment rapidly in mode B, and finally saturate in mode C. The micro-process of the mode transition shows that the discharging domain initiates at the edge of the hole (mode A), subsequently extends toward the center (mode B), and ultimately extends beyond the hole boundary (mode C). To further understand these transitions, finite element simulations and an equivalent circuit model of MHDBD are conducted, which reveal enhanced discharge strength and discharge area as the system progresses from mode A to mode B and C. The speculative mechanism of a mode transition involves the variation of the electric field distribution and the resulting acceleration of the electrons, and the following collision responses. Additionally, the effect of pulse frequency and hole diameter of the MHDBD on the mode transition conditions is also investigated, and the results show that higher frequencies are easier to prone mode transition, while large holes have fewer discharge modes.

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