Dynamics of Surface Streamer Plasmas at Atmospheric Pressure: Mixtures of Argon and Methane

A nonequilibrium atmospheric streamer discharge was investigated as a means to seed a large-gap arc breakdown. The dynamics of the streamer were analyzed with high speed imaging, photodiode light intensity, and current-voltage measurements. The temporal evolution of the discharge included a localized surface corona and a positive surface streamer. With the addition of an impurity gas (methane), the ionization was suppressed, which inhibited surface streamer propagation. The electron temperature was determined from time and spatially averaged spectra, coupled with a collisional-radiative model. The electron temperature in argon was measured at 1.25 eV for an electron density range of 10
¹⁹
- 10
²⁰
m
^-3
. Partial local thermodynamic equilibrium calculations showed that the Ar II 4p states followed a Boltzmann distribution with an excitation temperature of 0.7 eV. The gas temperature was estimated at 815 K from a black-body distribution. The velocity of the surface streamer in argon was estimated at ~100 km/s with a diameter of ~500 μm.