Study Of Self-pulsing Phenomenon In Atmospheric-pressure Plasma Jet

Atmospheric-pressure plasma jet(APPJ),as a typical kind of gas discharge generating low-temperature plasma,has been a hot research topic in plasma science and technology.For its advantages such as low operating temperature,active chemical properties,free of pollution,and so on,APPJ is promising for many fields of medical,material,and environment science.The stability of APPJ is the basis of the plasma processing technique.In this paper,we present experimental study on the self-pulsing phenomenon based on atmospheric-pressure plasma jet(APPJ)in a hollow electrode configuration driven by dc voltages.Firstly,the characteristics of the self-pulsing in gas flow induced APPJ in hollow electrode are investigated experimentally.The current-voltage curve,the typical waveforms of current and voltage of self-pulsing,the time-resolved images,and the repetition frequency are measured under different experimental conditions.The results show that the APPJ of a hollow electrode can sustain in a stable,repeatable self-pulsing regime.The waveform of the pulsed current is very stable with nearly constant rising and decay time at different discharge averaged currents.However,the pulse interval,which determines the pulse frequency,depends on the discharge conditions.The pulsing frequency increases linearly with the averaged current and the gas flow rate,but decreases with the electrode gap.The time-resolved images recorded by an ICCD camera show that a pulsed process of APPJ of a hollow electrode contains the evolutions of gas breakdown,discharge development,and decay of a glow plasma.A weak discharge is maintained during the time interval between two pulses,indicating that the self-pulsing in this APPJ is a mode transition between glow and weak discharge.Secondly,an equivalent electric circuit consisting of a variable resistor and capacitor is employed to describe the self-pulsing in the gas flow induced APPJ.In this model,the variable resistor represents for the equivalent nonlinear resistor of the discharge plasma,while the capacitance for the equivalent capacitance of the discharge cell.The whole discharge process includes the charging of the capacitor and the discharging of the capacitor through the resistor,resulting in a varied current that increases significantly and then decreases subsequently,through which the pulsed form of the discharge and the transition of discharge mode are yielded.The model can well explain the self-pulsing in this discharge system.