Single-electrode He microplasma jets driven by nanosecond voltage pulses

Excited by 5 ns, 8 kV voltage pulses, a 260 μm-diameter, 8 mm long helium plasma jet was generated with a single-electrode configuration in ambient air. Application of fast high voltage pulses (≥1012 V s−1) resulted in rapid acceleration of the microplasma plumes; within 5 ns the plume velocity reached 8 × 105 m/s, almost three times higher than that of the plasma jet generated with the pulsed voltage of the same amplitude but with a lower increase rate (1011 V s−1). Importantly, the ultrashort electric pulses were able to efficiently deposit energy in the plasma during the initiation process, which may be responsible for the rapid acceleration of the ionization wavefronts during the streamer onset, as well as efficient production of reactive plasma species including O(5P) and N2+(B2Σu+) via electron-induced processes. Emission spectral comparison between the plasma jets excited with 5 ns voltage pulses and with 140 ns voltage pulses showed enhanced O(5P) and N2+(B2Σu+) emission by the shorter pulses than the longer ones, while the vibrational and rotational temperature for both plasma jets are at 3000 K and 300 K, respectively.