Trapped Electron Effects in Transient Helium Sub-Nanosecond Atmospheric Microplasmas

For fast rising voltage in planar electrode geometry, it is shown that electrons can be trapped in a potential well between a reversed plasma-driven electric field and the applied electrode voltage. This trapping mechanism occurs in a subset of the inter-electrode gap and leads to increased average electron density in nanosecond discharges. There is a threshold ratio of the applied voltage to rise time for which the electrons experience a pendulum-like motion without any polarity change in the applied voltage. The fast rise time of the driven voltage leads to an enhanced trapped effect and augments the electron density of >5 eV energetic electrons, which can be exploited to produce excited chemical species and high plasma densities on nanosecond timescales.