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Two modes of a plasma jet excited by a direct current voltage

A plasma jet excited by a direct current voltage is developed to generate a diffuse plasma plume by blowing atmospheric pressure argon. Results show that the plume discharge operates in a single-pulsed mode or a continuous one depending on the applied voltage. For the single-pulsed mode, the discharge frequency increases with increasing the applied voltage or the air concentration, while it keeps almost constant with increasing the argon flow rate. The discharge dynamics at the breakdown stage indicate that the light emission propagates along the gas flow at a velocity in the order of 104 m s−1. The spatially resolved emission intensity at the afterglow stage of the pulsed discharge manifests a stratification into dark and bright luminous regions along the gas flow. For the continuous mode, however, the emission intensity gradually decreases along the gas flow. It is found that the continuous discharge is in a Townsend discharge regime judged from both the positive slope of the voltage–current curve and the small current density on the cathode surface. Based on optical emission spectroscopy, excited electron temperature and gas temperature of the plasma plume are obtained by a Boltzmann plot and fitting the spectra of OH radicals, respectively.