Investigation on the streamer propagation in atmospheric pressure helium plasma jet by the capacitive probe

In this letter,the streamer propagation in the atmospheric pressure helium plasma jet with afloating electrode nozzle driven by the kHz AC power supply is investigated.The current signal induced by the space charges and the mean propagation velocity of the guided ionization waves are measured by the capacitive probe method in the discharge region.The space charges in the guided ionization waves are found to increase with the applied voltage,which enhances both the electric field near the streamer head and the propagation velocity.The applicability of the streamer mechanism to the propagation of the guided ionization waves is validated by this electrical diagnostic method.

Ionization waves in nanosecond pulsed atmospheric pressure plasma jets in argon

Typical ionization waves(IWs)are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets(APPJs)with argon flow,combining both the measurement of the axial electric field(Ez)and the temporal resolved optical imaging.The movement of the luminous APPJ head is recognized as the development of the IW front,accompanied with the propagation of the peak electric field.Especially,the radial distribution of Ez transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front.As for the temporal Ez trend,there is a mode transition from the single-peak feature under a low peak voltage to the double-peak feature under a higher peak voltage,indicating the existence of both primary and secondary IWs.The effect of target conditions on the IWs in APPJs is also explored.With a metal target,no residual electric field is observed before imposing the high-voltage pulses.However,with a dielectric target,the residual surface charges generate a back-ground electric field in the opposite direction to that during IW propagation.In the free APPJ(with no target),on the voltage falling edge,a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propa-gation on the voltage rising edge.