| Atmospheric pressure low-temperature plasma jets, which can generate room temperature plasma in open space rather than in a confined discharge gap and have very simple configure structures, are recently a topic of great interest in the filed of plasma. They consist of a variety of active agents and have strong chemical feature. So plasma jets are favorable for applications such as biomedical, material processing and so on. In this thesis, some advanced atmospheric pressure low-temperature plasma jets are developed regarding the problems such as the plasma plumes cover only a few square millimeters and rely on external powerand gas feed supply. What’s more, the key active agents (O3molecule, OH radical, O atom) are diagnosed in the plasma jets. The generation process, development law and density distribution of these active agents are investigated. It provides an important reference to the plasma jets’ applications. The main contents are as follows:1. Development of atmospheric pressure low-temperature plasma jet which can generate large-scale plasma plume. The source is consisting of ten small plasma jets to form a plasma jet array. It is very easy to form larger-scale plasma plume using this method.High-speed photographs show that the propagation speed of each plasma plume is not the same. At the beginning, the propagation speed of the plasma plume on both edges is higher than that in the middle of the plasma array. The simulation results indicate that this is due to the electric field distribution of the plasma array.It may help us to design a new homogeneous and large-scale cold plasma source for various applications.2. Development of portable atmospheric pressure low-temperature plasma jet. Two kinds of battery-operated, handheld air plasma jets are developed which are named "Plasma Flashlight" and "Plasma Wand".(ⅰ)"Plasma Flashlight" is driven by a12V DC battery and does not require any external generator or wall power. Neither does it require any external gas feed or handling (e.g., valves, mass flow controllers, etc.) system. It is the first portable atmospheric pressure low-temperature plasma jet reported till now. The outer diameter and the length of "Plasma Flashlight" are4.5cm,respectively. The plasma plum (2cm2) can be touched without any feeling of warmth or electrical shock.(ⅱ)"Plasma Wand"also isa battery-operated handheld surface DBD plasma source which is designed for the treatment of narrow and deep channels such as nasal cavity.(ⅲ)"Plasma Flashlight’ has demonstrated superior performance in inactivation of a25.5μm thick Enterococcus faecalis biofilm, which is10.5microns thicker than the previously reported one. The preliminary bacteria inactivation experiment results show that all bacteria samples on the microfiltration membrane are killed by "Plasma Wand" within30s."Plasma Wand" has very high sterilization efficiency.3. Diagnostic investigations on the active agents of the plasma jet using optical emission spectroscopy (OES) and optical absorption spectroscopy (OAS).(ⅰ) The optical emission spectra of air plasma jet are dominated by the excited N2, N2+and the active O species. If the He is used as the working gas, the excited O, OH, N2and He are exist in the plasma plume. It is well knownthat species such as O and OH are very active.(ⅱ) The ozone density is about120ppm at1mm away from the plasma rod.4.Diagnostic investigations on the OH radicals of the plasma jet usinglaser induced fluorescence (LIF).(ⅰ)The temporal and spatial OH radicals concentration of the atmospheric pressure low-temperature plasma jetare investigated using LIF imaging. It is found that the OH radicals are mainly produced two times during the voltage pulse, once after the primary discharge and again after the secondary discharge.The OH generated by previous pulses can accumulate and the gas flow can blow the OH generated inside the discharge tube to the detected region.(ⅱ)It is found for the first time that the OH LIF signal intensity in the plasma plume is much stronger on both edges, which indicates that the OH radicals have a donut-shaped distribution.(ⅲ) An improved model for estimating the absolute density of OH radicals in plasma jet is present. In this model, both the main loss mechanisms of OH by chemical reaction and the effect of gas flow are taken into account. An absolute OH density of2.4×1013cm-3at5mm away from the nozzle and1μs after the discharge gives a best fit between the measured OH LIF decay signals and the simulation results from the model.(ⅳ) It is found that the OH density increases linearly with the applied voltage in the range of4kV to9kV.On the other hand, the OH densities increase with the increase of the pulse frequency, but not linearly. The variation of pulse width does not affect the density of OH radicals noticeably.(v) The humidity of the working gas is crucial to generate OH radial in plasma jet. Theabsolutedensity of OH reaches to maximum value when the humidityof the working gas is120ppm. Theenvironment humidity around the plasma plum is not expected to play a significant role in thegeneration of OH.(5) Diagnostic investigations on the O atoms of the plasma jet using two-photon absorption laser induced fluorescence (TALIF).(ⅰ)O atoms in the plasma jet are also mainlyproduced by the rising edge discharge and failling edge discharge. The gas flow can blow the O atoms inside the plasma plume to the downstream. O atoms can exist in the plasma jet for a long time which is about20ms.(ⅱ)At the high discharge frequency condition, the O atomsdistribute uniformly inside the cross-section of plasma plume. However, actually the O atoms are generated around the plasma plum according to the single pulse discharge.(ⅲ) O2density in the working gas is crucial to generate O atoms in plasma jet. A maximum of the atomic oxygen density is observed for0.3%molecular oxygen admixture. |
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