Properties of an atmospheric He-based nanosecond jet discharge

An atmospheric repetitive discharge with 10 ns current pulse width and 3×10¹¹ V/s voltage growth rate operating in jet geometry in He with admixtures is studied by optical emission spectroscopy methods. The measurements were employed in the discharge, post-discharge and jet regions. Rotational and vibrational temperatures of the excited discharge molecules, the electron density (N_e) and the electric field (E-field) were measured. It is found that N_e reaches nearly 10¹⁶ cm^-3 in the plasma pulse. Upon more careful fitting, it was found that H_β line reveals double-Lorentzian profile corresponding to two electron density groups. The low-density group contains density below 10¹⁴ cm^-3 showing no decent trends, whereas the high-density group shows a clear density decay after the peak (avalanche). The high-density electron cloud leads to formation of a microscopic E-field of about 30 kV/cm between the electrodes right after the pulse. At the same time, in the discharge tube the E-field is directional with slight domination of radial component. Its value is roughly twice lower as compared to the one found in the discharge area. The gas temperature does not exceed about 320 K during the whole discharge cycle. All in all, the low gas temperature, high peak electron density, fast ionization wave propagation and the accompanying directional electric field make ns- jet discharges good candidates for remote surface treatment.