Numerical Simulation On Discharge Breakdown Characteristics Driven By Pulse-modulation Radio-frequency Sources With Fluid Model

The atmospheric pressure pulse-modulated low-temperature plasma has been widely concerned and studied in recent years because of their convenient applications without using a vacuum device.It can suppress the rise of the background gas temperature,and can generate a large amount of active particles.The pulse modulation parameters have a great influence on the breakdown characteristics of atmospheric pressure low temperature plasma.By studying the influence law of modulation parameters,suitable modulation parameters can be selected to obtain a stable plasma.In this paper,the fluid model is used to study the atmospheric pressure low temperature plasma breakdown characteristics.By comparing with the experimental results,the four coupling power modes of plasma at the beginning of pulse modulation are studied systematically.The plasma coupling power caused by different applied voltages and modulation parameters is systematically studied.The way the mode changes,the effect of the modulation parameters on the breakdown delay,and the effect of the modulation parameters on the breakdown voltage and the mode switching voltage.The main conclusions are as follows:In the atmospheric pressure dielectric barrier discharge,when the applied voltage reaches the breakdown voltage,the plasma coupling power exhibits four typical modes.When the modulation frequency is small,the turn-off time is long,and the"pre-discharge" plasma is required.The coupling power starts;as the modulation frequency increases,the turn-off time decreases,the "pre-discharge" phase disappears,and the plasma begins to couple power at the beginning of the pulse period;when the modulation frequency is further increased,the turn-off time becomes small.At this time,the"first pulse"phenomenon occurs,and the plasma coupling power is large at the beginning of the pulse;when the modulation frequency is further increased,since the number of RF cycles applied during the pulse modulation period is too small,until the pulse turns off the air gap The voltage and conduction current also fail to reach a stable value.An increase in the applied voltage causes a mode transition in which the breakdown mode can be coupled to more power at the beginning of the pulse.The increase of the modulation frequency and the increase of the duty cycle will reduce the pulse off time.Under the same applied voltage,the smaller the off time,the greater the plasma coupling power at the beginning of the pulse,thus reducing the breakdown delay.When the number of RF cycles applied during the fixed modulation period,the breakdown voltage and the mode switching voltage increase with the increase of the pulse off time;when the fixed pulse is turned off,the breakdown voltage and the mode conversion voltage will follow the modulation period.The number of applied RF cycles decreases as the number of applied RF cycles increases.Increasing the duty cycle increases the number of RF cycles applied during the modulation period and shortens the pulse turn-off time,thus reducing the breakdown voltage and mode switching voltage.When the duty cycle is fixed and the modulation frequency becomes larger,it is equivalent to reducing the pulse off time and also reducing the number of RF cycles applied during the modulation period.When the modulation frequency is between 100kHZ and 500kHz,the pulse off time dominates.Increasing the modulation frequency makes the pulse turn-off time shorter,so that the breakdown voltage becomes smaller.When the modulation frequency is from 600kHZ to 100kHz,the number of RF cycles applied during the pulse modulation period predominates,and the modulation frequency is increased to be applied within the pulse modulation period.The reduction in the number of RF cycles will increase the breakdown voltage;a minimum value of breakdown voltage will be generated around 500 kHz.The number of RF cycles applied during the pulse modulation period has a greater influence on the mode conversion voltage.When the modulation period is small,the mode conversion voltage does not change much.When the modulation frequency is greater than 500 kHz,the mode conversion voltage starts to increase as the modulation frequency increases.The time is mainly because the modulation frequency increases and the number of RF cycles decreases during the modulation period,thereby increasing the mode switching voltage.When the background frequency reaches the very high frequency and the discharge gap is reduced,the breakdown voltage varies little with the modulation frequency,but the breakdown voltage decreases as the duty cycle increases.