A Study On Improving The Homogeneity And Stability Of Atmospheric Pressure Air Plasma

Non-equilibrium plasma has a lot of active particles, such as electrons, metastable ions, andradicals. It has strong reactive activity. In non-equilibrium plasma the electrons energy is veryhigh that may be beyond 10 eV, but the ions energy is very low that may be several thousands ofK, even room temperature, so the reactive threshold may be reduced, many reactions can occurin low temperature. Non-equilibrium plasma has a lot of charged particles, in which the mass ofelectrons and ions is very different, the energy distribution is anisotropy, so the energy flowdirection can be controlled by external electric and magnetic fields flexibly. Due to the meritsmentioned above non-equilibrium plasma has been applicated widely. Atmospheric pressure airnon-equilibrium plasma, such as corona discharge, dielectric barrier discharge and glowdischarge plasma does not need vaccum systym and noble gas, so the operating cost is reducedobviously, its prospect is very good. Because of the positive feedback characteristic of plasmadischarge development process and the particles density of atmospheric pressure gas is high,discharge is easy to transit to spark even arc, so the homogeneity and stability of plasma is veryimportant for its application, which has been a hot topic in plasma field. To improve thehomogeneity and stability of non-equilibrium plasma in atmospheric pressure air, the followingwork is done in this paper:1. Resisrance and Capacity-Coupled Glow Discharge for plasma generation method isproposed. According to the principle of Resisrance and Capacity-Coupled negative feedbackprinciple an anti-electric field is formed by the coupled capacitors, which can extinct thedischarge gradually; The coupled resistance can increase the time constant of the circuit andresist the high frequency oscillation caused by discharge, so the transition from glow to sparkcaused by the positive feedback mechanism of plasma development is prevented successfully, astable atmospheric glow discharge in static air is produced by using pin-to-pin, pin-to-plate, andpin-to-water generators, respectively. The increase of coupled capacity reduces the maximumvoltage for sustaining glow discharge. It exsists an optimal range with respect to the influence ofcoupled resistance on discharge stability. The influence of coupled resistance and capacity ondischarge is determined by the time constant of the circuit. According to the range for optimalgeneration of glow discharge the sequence is pin-to-pin, pin-to-water, and pin-to-plate generator,respectively. The transformation from spark discharge to diffuse corona discharge inatmospheric air is found in some conditions with a capacity coupled pin-to-water plasma reactor. The influences of power source frequency, inter-electrode gap, and coupled capacitance on thetransition are investigated. The reason for this transition is discussed.2. A study on improving the homogeneity of current pulse in DBD using active impedancegenerated by a magnetic compression coil is done. The peak current of DBD is reducedeffectively when the voltage is low. The intensity of optical emission spectra (OES) droped, andthe vibrational temperature of gas increased. On this basis DBD without filamentary pulse isproduced when a coupled resistance is introduced to the circuit. It is a weak DBD in the nature.The active impedance and the coupled resistance can change not only the current waveform butalso the nature of plasma. It has a profoundly effect on plasma. The intensity of DBD plasmamay be modulated by this method, so the application range of DBD plasma may be enlarged.3. The influence of a longitudinal dielectric on nanosecond pulse gas discharge is examined.An appropriate longitudinal dielectric tube can enhance the homogeneity, enlarge the scale ofplasma, the maximum ratio 2 is reached, the intensity of OES reduces to 29% of the original one(no dielectric is used). The homogeneity of discharge was enhanced further when a coupledcapacity is used. The longitudinal dielectric has no obvious effect on discharge using analtenative current power source. The reason should be ascribed to the difference of plasmatemperature caused by the two power sources, the constriction of discharge channel is found andthe scale of plasma is not enlarged when an altenative current power source is used.