Electron densities and temperatures of an atmospheric-pressure nanosecond pulsed helium plasma jet in air**{Electron properties in a nanosecond pulsed atmospheric plasma jet determined by laser Thomson scattering}.

Abstract

We report temporally and spatially resolved electron property measurements of a 150 ns pulsed helium plasma jet in air operated at a low-repetition rate using Thomson laser scattering. A ring-shaped electron density distribution was revealed in the pulsed plasma jet at an axial distance of 1 mm from the electrode nozzle and started to converge after 5 mm. A peak electron density of 1 × 1020 m−3 was identified at the radius of the ring and close to the nozzle electrode. For a delay time ranging from 60 to 250 ns after the onset of the streamer, the electron temperature at the radius of the ring varied from 2.8 to 0.8 eV. Higher temperature >3.5 eV was also identified at regions with lower densities. Importantly, temporal development of the electron density and temperature of the plasma jet confirmed the strong dependence of guided streamer formation and propagation on the external pulsed electric field. The jet current measured during the rising and falling phases of the voltage pulse can be related to the peaks in the temporal development of the electron density.