Investigation of dynamic evolution and emission pattern transition in an atmospheric pressure surface micro-discharge

This study investigates the dynamic evolution and emission pattern transition of atmospheric-pressure helium surface micro-discharges using optical emission spectroscopy and electrical measurements. Utilizing an asymmetric electrode configuration, multiple short-duration microdischarges are observed during the negative half-cycle, while the positive half-cycle is dominated by a single high-current streamer discharge that determines the overall emission profile. With increasing applied voltage, a periodic transition between symmetric and asymmetric discharge patterns occurs, accompanied by a non-monotonic variation in peak discharge current. This behavior is attributed to the memory effect of surface charges and the influence of the applied electric field. The transition process unfolds in three distinct stages: an initial symmetric discharge pattern with increasing current, sustained by a uniform distribution of surface charges aligned with the electric field; a transitional phase where symmetric and asymmetric patterns coexist while the current declines, reflecting a reorganization of surface charges; and a stabilized asymmetric pattern with recovering current, driven by a localized, non-uniform surface charge field. Moreover, plasma propagates asynchronously across a hexagonal mesh electrode array. Ignition starts within individual mesh units and spreads progressively to neighboring units at an estimated velocity of about 2.25 × 104 m/s. During the positive half-cycle, the propagation direction reverses compared to the last discharge event of the previous negative half-cycle, due to the electric field polarity reversal and the residual surface charge distribution. These findings provide valuable insights for the design and optimization of surface micro-discharge devices in biomedical applications.