| Atmospheric-pressure plasma jets(APPJs)extend the applications of plasma,and the propagation of the guided ionization waves(IWs)associated with the APPJs has attracted a considerable attention.The propagation of the IWs is a process of macroscopic physical states caused by the micro effect.Due to the limitation of the diagnostic techniques for atmospheric-pressure plasma,the study of the propagation of the IWs may contributes to analyze the mechanism of the IWs.Therefore,conducting the experimental study of the IWs could be with both scientific significance and application value.In this thesis,by using spatio-temporal resolution image measurement,optical emission spectroscopy(OES),and electrical measurement,the propagation of the IWs under different discharge parameters,pulse sequences,electrode configurations and geometrical constraint conditions was investigated.The main results are as follows:The IWs generated by a tunable AC power supply or DC pulsed power supply propagated inside a quartz tube with an inner diameter of 2.0 mm and gas gap distance of 85 mm was studied by changing the basic discharge parameters.Firstly,our measurements show that the propagation of the IWs is strongly dependent on the value of applied voltage(Vapp)and gas flow rate(Qv).It was found that the IWs could be generated in the dielectric tube,then propagate along the dielectric tube and finally breakdown the gas gap with increasing Vapp.The calculations show that the propagation velocity of the IWs increased with an increase in Vpp,and the propagation of the IWs generated by DC pulsed power supply was faster than that generated by AC power supply.The above results suggest that the waveform of the applied voltage.Vpp and the distribution of the charged particle in the tube play a crucial role on the propagation behavior of the IWs.Secondly,our measurements show that the propagation velocity of the IWs was decreased when the Q,increases from 150 sccm to 10000 sccm.The OES measurement shows that the spectral intensity of N2 and N2+ was obviously increased when Qv decreases,which indicates that a small amount of air was diffused into the tube.Further analysis indicates that penning ionization may play a critical role on facilitating the propagation of the IWs.Thirdly,when the pulse repetition rate increased from 10 Hz to 5000 Hz,the propagation of the IWs did not show much depend on the repetition rate.In order to clarify the effects of residual charges and long-lived species on the IW propagation,the repeatability of the IWs.the propagation behaviors of the IWs during the falling phase of the voltage pulse,the propagation behaviors of the IWs in the pulse sequence with different pulse-off time and the ignition voltage was studied in a series of burst voltage pulse.Firstly.When the pulse interval time was 5 s,our measurements show that the propagation of the IWs always behaved in a repeatable pattern along the dielectric tube,which suggest that the IWs could be generated and propagate in a repeatable pattern along the dielectric tube with a very low density of seed electrons.Secondly,our measurements show that the propagation of the IWs during the falling phase of the voltage pulse was strongly dependent on the pulse width,and after the falling edge of the voltage pulse,the applied voltage falls to 0 V,but the propagation of the IWs continues.Thirdly,for a longer pulse-off time(100 ?s-190?s),the propagation velocity of the IWs was decreased from the 1st to the 10th HV pulse,then increased after the 10th pulse,and finally become stable after about 500 pulses.When the pulse-off time is reduced to 15 ?s.the propagation velocity of the IWs rapidly increases and becomes stable after the 1st HV pulse.Fourthly,the ignition voltage was significantly reduced from 3.5 kV to 1 kV with decreasing the pulse-off time from 5 s to 5 ?s.Consequently,the above results suggest that the accumulation of surface charges,the residual charges,and the long-lived species play a crucial role on the propagation of the IWs during the initial stage of the pulse sequence.The accumulation of these species tends to be balanced after a certain amount of pulses and finally the propagation of the IWs becomes stable.Based on the model of the extend of operating range of the APPJs by using the floating electrode,the propagation of the IWs along the quartz tube before and after the floating electrode with varied length and diameter was studied.Our measurement show that the propagation velocity and maximum emission intensity were obviously increased with the increase of the floating electrode from 80 cm to 1000 cm.However,when the diameter of the floating electrode increased from 1.0 mm to 2.8 mm,the propagation of the IWs did not show any depend on the diameter.The equivalent circuit was built to analyze the effect of the floating electrode on the propagation of the IWs.and the analysis suggest that the inductive effect of the floating electrode play a critical role on the propagation of the IWs in such discharge model.In addition,the effect of the external high voltage electrode wrapped around the dielectric tube on the propagation of the IWs was studied.Our measurements show that the propagation of the IWs was strongly dependent on the potential of the external electrode.When the potential was positive,the propagation of the IWs was suppressed,however,the propagation velocity was increased in the vicinity of the external electrode.On the contrary,the propagation was facilitated when the potential was negative.Our analyses suggest that the external electric field could affect the electric field of the front of the IW,and the potential of the external electrode could change the inner surface charge distribution.Therefore,the propagation of the IWs exhibits different patterns with varied external electric field.The propagation of the IWs inside different shape and size of the dielectric tube was studied.Firstly,the propagation of the IWs inside a U-shape tube was studied.Our measurements show that the IWs tended to propagate along one side of walls rather than filling the channel,which is different with that in the straight tube.Furthermore,the propagation velocity of the IWs was decreased when the curvature of the bend decreased from 28 mm to 16 mm.Our analysis suggests that the component of electric field whose direction is perpendicular to the walls provides a constraining force to the IWs in perpendicular direction,and thus the IWs propagate along one side of the tube in the bend part,and the electric field generated by the HV electrode suppress the propagation of the IWs after the bend.Secondly,the propagation of the IWs inside a tapered tube was studied.Our measurements show that both the intensity and velocity of the IWs decrease dramatically when they propagate to the tapered region.After the taper,the velocity,intensity,and electron density of the IWs are improved with the tube inner diameter decreasing from 4.0 to 0.5 mm.Our analysis indicates that the local gas conductivity and surface charges may play a role in the propagation of the IWs under such a geometrical constraint,and the difference in the dynamics of the IWs after the taper can be related to the restriction in the size of space charge layer in IW front. |
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