| As the continuous development of non-thermal plasmas in many practical applications, more stringent requirements have been put forward about non-thermal plasma technology. In the past, most kinds of non-thermal plasmas were produced in low pressure or inert gas environment, and it was necessary to be equipped with complex and awkward system or inert gas bottle for plasma generator. These methods not only increased the cost of the actual application, but also limited its applications. Although non-thermal cold plasmas can be obtained at atmospheric pressure in the air by inserting dielectric barrier between the electrodes (DBD), two problems are inevitable. The dielectric barrier is likely to produce pollution to plasma, and plasmas are often limited in a narrow gap. In recent years, with the rapid development of pulsed power technology, some researchers have tried to introduce pulse power technology into the field of non-thermal plasmas. They wanted to get non-thermal plasmas at atmospheric pressure in the air, which is directly excited by high-voltage repetition-frequency nanosecond pulses (i.e. atmospheric-pressure air diffuse discharge). Usually, these pulses are produced by a set of multistage magnetic compression device. More and more attention is attracted on this method, because it can get rid of the inert gas, vacuum equipment and dielectric barrier. However, through extensive research, it was found that this kind of non-thermal plasma was extremely unstable. Arc filaments were easy to come out and the discharge transformed from non-equilibrium to equilibrium state. Moreover, at present, the discharge area was still narrow by this method, and the uniformity was less satisfying. Thus, it is necessary to make further research on its discharge mechanism, discharge characteristics, practical application, etc. Taking the atmospheric pressure air diffuse discharge as research object, this thesis mainly carried out the following areas:Firstly, aiming to produce a stable atmospheric-pressure air diffuse discharge, this thesis designed a repetition-frequency nanosecond pulse generator. Instead of expensive multistage magnetic compression device, the pulse generator was mainly made by a Tesla transformer and a gas sharping switch. Based on the pulse generator, this thesis manufactured a set of atmospheric pressure air diffuse plasma generator. The peak voltage and pulse rise time was65kV and30ns, respectively. The repetition frequency changed from1to500Hz, and the full width at half maximum was as high as750ns. Using wire electrode configuration, the diffuse plasmas were successfully produced at atmospheric pressure in the air. This broke through the conclusion that diffuse plasmas can be produced only when stimulated by the pulses of very narrow pulse width (several to tens of nanoseconds).Secondly, with the help of electrical, optical, and spectroscopy measurements, this thesis analyzed the physical mechanism of repetition-frequency nanosecond pulse discharge in the line-line electrode configuration. Effects of electrical parameters and wire electrode configurations on the discharge morphology, discharge mode, uniformity and stability of diffuse plasmas were investigated. The related results demonstrated that long wire electrodes were suitable for suppressing the arc filaments, and short wire electrodes were fit for enhancing the energy in the discharge area. This provides new clew to obtain large-scale diffuse plasmas. In order to study the plasma activity and uniformity, optics emission spectrum were measured to study the vibrational temperature, rotational temeperature, and the spatial distribution of light emission intensity. Based on different discharge development process, four stages were divided inter the discharge gap. By analyzing the spectroscopy characterisctics in different stages, the methods to improve discharge stability and uniformity were put forward.Thirdly, based on the self-designed repetition-frequency nanosecond-pulse generator, the possibility of obtaining three-dimensional large-scale diffuse plasmas was discussed in the wire electrode array configuration. Diffuse plasmas were obtained in cross-parallel wire-electrode-pair configuration, a cylindrical diffuse-plasma chamber, and a totally-enclosed plasma cage. Specifically, the discharge volume in the first electrode configuration was as large as18×15×15cm3, and can be extended in three-dimensional spacing by using more and longer wire electrodes. The diameter of the cylindrical diffuse-plasma chamberwas8.0cm, and can be extended in the height direction by using longer wire electrodes. Also, related plasma properties were analyzed in this thesis.Lastly, taking nylon fiber cloth as treatment object, effects of diffuse plasmas on the nylon fiber surface were investigated in different discharge parameters. The physical and chemical change on the surface were measured using wicking effect, atomic force microscopy (AFM), scanning electron microscope (SEM), X-ray photoelectron spectrometer (XPS). Then, taking the E.coli as experiment strains, the bactericidal performance was studied under the diffuse plasmas treatment in different discharge parameters. After severalseconds’treatment, perfect hydrophilicity was attached on the nylon surface and the number of e.coli colonies was also greatly reduced. All of them proved that there was high practical application value for the diffuse plasmas in the wire electrode array configuration. |
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