| Cold plasma jets generated in atmospheric pressure discharges represent a rapidly developing technology of non-thermal atmospheric pressure plasma sources, which have attracted much attention in recent years. Their desirable properties, including high reactive chemical species (e.g. ions, electrons, excited atoms, molecules, and free radicals), low temperature, simplicity of operation, faster treatment, lower cost, and chemical waste free, have made them unique and promising for a number of important industrial applications, such as biomedical engineering, environmental engineering, plasma chemistry, and material processing, especially materials which are sensitive to temperature. Besides, due to the spatial separation of their generation from their application regions, cold plasma jets are less influenced by the downstream sample, which make them ideally applicable for material with uneven surfaces particularly. To improve the performance of atmospheric pressure cold plasma jets and understand their characteristics better, the following work is done in this paper:1. A hybrid capillary-ring cold atmospheric jet is proposed, in which the barrier-jet discharge plasma is initiated between a powered capillary electrode with a helium flow and a downstream concentric grounded ring electrode. The characteristics of the jet discharge are studied by means of the electrical and spectroscopic diagnosis. And the results demonstrate that low breakdown voltage and high atomic oxygen production are achieved simultaneously, and these features are mainly attributed to the hybrid configuration of capillary-ring electrodes.2. A simple device with a floating electrode configuration to generate a cold atmospheric argon plasma jet is studied. The floating electrode plasma jet has identified a number of desirable features including low gas temperature, low operation voltage, and high stability. The results show that the improvement of the electrode configuration is effective in concentrating efficiently electrical energy into the discharge channel as well as controlling directly the discharge intensity of the jet, therefore making the generation of the argon plasma jet simpler and more effective.3. A dual-frequency cold atmospheric pressure plasma jet is studied as a possible route to separate control of basic plasma parameters particularly plasma density, plasma plume length and gas temperature. With spatially separate application of two excitation frequencies, one at 5.5 MHz and the other at 30 kHz, plasma dynamics exhibit interaction between influences by the two individual excitation frequencies. It is shown that the upper stream discharge at 5.5 MHz feeds abundant electrons to the downstream plasma plume sustained at 30 kHz for the latter to acquire high plasma density and long plume length without much increase in its gas temperature.4. A hitherto unreported class of self-organized pattern is observed in a wide atmospheric pressure plasma jet with a dielectric barrier discharge (DBD) configuration established in a helium flow. Under different experimental conditions, the plasma jet has been shown to evolve through three modes having diffuse, regularly self-organized and completely disordered discharges respectively. The influences of experimental conditions on the mode transition are investigated, and the reason for the pattern formation is discussed. These observations will enrich the understanding of pattern formation in DBDs and give additional information for developing a physical model of pattern formation in DBD systems.5. The jet array with a group of atmospheric pressure cold plasma jets densely arranged in a honeycomb-like configuration is studied, in which a hybrid capillary-ring cold atmospheric jet is used as the element component. It is shown that the jet array is applicable to produce uniform plasma over a larger area and presents high jet density, good jet-jet uniformity, and robust plasma stability. Besides, a 7 jet array is especially studied by means of the electrical and spectroscopic diagnosis as well as the test of sterilization, which provides possible insights to better control the jet-jet interactions and further the study of scalable plasma jet array.
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