Optical Spectra Characteristic And Application Basic Investigations Of Nanosecond Pulsed Dielectric Barrier Discharge At Atmospheric Pressure

Nanosecond pulsed discharge plasma has become a hot field in low temperature non-thermal equilibrium plasma area because of its unique advantages such as high energy effective, good discharge uniformity, high electron temperature and low gas temperature. In this paper, bipolar nanosecond high voltage pulse with20ns rising time is employed to generated uniform or diffuse dielectric barrier discharge using needle-plate, multiple needle-plate, and plate-plate electrode configurations in nitrogen and air at atmospheric pressure. The main research content is described as follow:1. In needle-needle electrode configuration, bipolar nanosecond pulse voltage is employed to generate diffuse dielectric barrier discharge plasma with low gas temperature. The diffuse dielectric barrier discharge can be obtained in large range of electrode gap distance, pulse peak voltage, and pulse repetition rate. The optical emission spectra, the time resolved spectra of N2(C3Πuâ†'B3Πg,0-0,337.1nm) and the waveform of are recorded under severe electromagnetic interference. The gas temperature is calculated by fitting the first negative bands of N2+(B2Σuâ†'X2Σg+,0-0). It is found that there are two different breakdown modes existing in positive and negative pulse discharges. In positive pulse discharge, the lagged time between the photocurrent pulse and the voltage pulse is about80ns and keep almost constant with the rising of pulse peak voltage. However, in negative pulse discharge the lagged time is much longer and decreases sharply with the rising of pulse peak voltage. In addition, the effect of oxygen in air on the diffuse discharge is studied; it is found the oxygen is not benefit to improve both the uniformity and the discharge intensity in nanosecond pulsed dielectric barrier discharge.2. Large area air diffuse nanosecond pulsed discharge can be obtained by using double needle-plate and multiple needle-plate electrode configurations at atmospheric pressure. Both double needles and multiple needles electrode configurations nanosecond pulsed dielectric barrier discharge are investigated. It is found that plasma volume increase with the rising of the pulse peak voltage but keep almost content as increasing of pulse repetition rate. In addition, both double needle-plate and multiple needle-plate electrode configurations with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma. It is found that the equivalent needle-plate electrode gap is unnecessary in nanosecond pulsed dielectric barrier discharge, which show the discharge can be used in the material modification of topographically non-uniform surface.3. In plate-plate electrode configuration, a homogenous dielectric barrier discharge plasma with very low gas temperature is obtained by using nanosecond bipolar pulse voltage with20ns rising time both in nitrogen and air at atmospheric pressure. The images of the discharge, the waveforms of pulse voltage and discharge current, and the optical emission spectra emitted from the discharge are recorded successfully under severe electromagnetic interference. The effects of the pulse peak voltage, the pulse repetition rate, and the gap distance between electrodes on the gas temperature and the emission intensities of NO (A2Σâ†'X2Π), OH (A2Σâ†'X2Π), and N2(C3Πuâ†'B3Πg) are discussed. It is found that the emission intensities of NO (A2Σâ†'X2Π), OH (A2Σâ†'X2Π), and N2(C3Πuâ†'B3Πg) rise with increasing both the pulse peak voltage and the pulse repetition rate but decrease with gap distance between the electrodes when it is larger than2.5mm. The effect of concentrations of O2on the emission intensities of NO (A2Σâ†'X2Π), OH (A2Σâ†'X2Π), and N2(C3Πuâ†'B3Πg) are also investigated, and it is found both the emission intensities of NO (A2Σâ†'X2Π) and OH (A2Σâ†'X2Π) reach maximum values when O2concentration is0.3.4. Nanosecond pulsed discharge is used for surface modification of polypropylene non-woven fabric and plasma mutagenesis of fungi and actinomycetes at atmospheric pressure. In the treatment of polypropylene non-woven fabric, compared with the DBD plasma excited by sine AC voltage, the nanosecond pulsed dielectric barrier discharge exhibits obvious advantages in improving the hydrophilic property of polypropylene non-woven fabric. The average energy cost is about20times lower than AC dielectric barrier discharge for improving the hydrophilic property of polypropylene to the same level. In particular, nanosecond pulsed dielectric barrier discharge plasma can treat the polypropylene non-woven fabric without any surface damage. In the plasma mutagenesis of microorganism, needle-cuvette and plate-plate electrode nanosecond pulsed dielectric barrier discharge plasma source are designed, and they are used to mutagenesis of fungi and actinomycetes in liquid state and solid state respectively for North China Pharmaceutical Co. Ltd..5. Homogenous dielectric barrier discharge is obtained in Helium at atmospheric pressure and the spatially resolved spectra of He (3s3Sâ†'2p3P), OH (A2Σâ†'X2Π), N2(C3Πu-> B3Πg), and N2+(B2Σuâ†'X2Σ+) emitted from homogeneous dielectric barrier discharge are recorded. The effects of applied voltage and driving frequency on the spatially resolved spectra of I Ie (3s3Sâ†'2p3P) are investigated, the formation mechanism of OH and N2+by the impurity in helium are discussed. It is found that the spatial distributions of the emission intensities of He(3s3Sâ†'2p3P), OH(A2Σâ†'X2Π), N2(C3Πuâ†'B3Πg), and N2+(B2Σu+â†'X2Σg+) exhibit two peaks at1and6mm from the upper electrode respectively in the7mm gas gap and the emission intensities at1and6mm are about2-3times higher than those at3-4mm, and most of the active particles are produced in the two regions. In addition, the impurity adding can lead to the change of discharge mode, when the concentration is in several hundred ppm, when the concentration is in several hundred ppm, the amplitude of the current pulse at the positive half-cycle is larger than that at the negative half-cycle, corresponsively, the asymmetric mode is presented by the spatial distributions of emission intensities of He(3s3Sâ†'2p3P), OH(A2Eâ†'X2Π), N2(C3Πuâ†'B3Πg), and N2+(B2Σu+â†'X2Σg+).