| Cold plasma jets generated in atmospheric pressure discharges represent a rapidly developing technology of non-thermal atmospheric pressure plasma discharges, which are one of the international research hotspots in plasma science and technical field currently. Compared with traditional discharge technology, one of the most prominent featured of the atmospheric pressure cold plasma jets is the spatial separation of their generation from their application regions, namely the high reactive chemical species (e.g. ions, electrons, excited atoms, molecules, and free radicals) produced in generation region are being transported to the application region. Besides, another attractive feature of the cold plasma jets is their enhanced plasma chemistry at low gas temperature. At present, their desirable properties, including low gas temperature, high chemical reaction activity, excellent controllability, simplicity of operation, have made them considerably promising for a number of important applications, such as traditional materials processing, surface modification, and emerging plasma medicine, environmental engineering, genetic engineering, especially for biomedical materials sensitive to temperature.It is of great importance to optimize the performance of cold plasma sources, diagnose the plasma discharge parameters, and study the basic physical process of the plasma discharge. Basing on these, the following work is done in this paper:1. An atmospheric pressure Ar/O2 cold plasma jet assisted by the preionization of syringe needle electrode discharge is proposed, which consists of the upperstream syringe needle electrode, the middle copper ring electrode, and the downstream ground plate electrode. A comparative study of three commonly used electrode configurations Ar/O2 plasma discharges are carried out basing on detail electrical and optical diagnostics. The experimental results show that the upperstream single needle argon discharge feeds abundant electrons and long-lifetime argon metastables atoms to the downstream Ar/O2 discharge for the latter to acquire uniform hybrid jet without much increase in its gas temperature. Utilizing the actinometry method to determine the concentration of atomic oxygen, it is found that there exists an optimal oxygen concentration in argon gas (0.9 vol%), at which most atomic oxygen are produced (about 1016-1017 cm-3). Finally, the Ar/O2 plasma jet is employed to clean out the heat transfer oil and a maximum cleaning rate of 0.1 mm/s has been obtained. 2. Characteristics of a double-power electrode dielectric barrier discharge of a high electron density argon plasma jet generated at the atmospheric pressure are investigated. Time-averaged optical emission spectroscopy is used to measure the plasma parameters, of which the excitation electron temperature is determined by the Boltzmann's plot method whereas the gas temperature is estimated using a fiber thermometer. Furthermore, the Stark broadening of the hydrogen Balmer Hβline is applied to measure the electron density, and the simultaneous presence of comparable Doppler, Van de Waals, and instrumental broadenings is discussed. Besides, properties of the jet discharge, including applied voltage, root mean square value of conducting current, and average absorbed power, are also studied by electrical diagnosis. It has been found that the electron densities in this argon plasma jet are on the order of 1014 cm-3, and the excitation temperature, gas temperature, and electron density increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate. This study provides a possible route to precise control of basic plasma parameters particularly electron density, electron excitation temperature and gas temperature.3. The effect of driving frequency in the 60-130 kHz range on the discharge characteristics of argon plasma designed with dual-power electrodes is further investigated based on the electrical (applied voltage, conduction current, and average absorbed power) and spectroscopic (gas temperature, the electronic excitation temperature, and electron density) diagnosis. It is shown that at constant applied voltage and gas flow rate, the increase of driving frequency in the range of 60-100 kHz exerts no significant influences on the preceding discharge parameters. While once the driving frequency exceeds a certain value of about 100 kHz, the discharge becomes intense abruptly and the corresponding discharge parameters increase drastically with the driving frequency. Detailed analysis about the effect of driving frequency on discharge characteristics is presented and two different dominant electron loss mechanisms, namely transport-dominated loss and diffusion-dominated loss, are proposed to account for the distinct effects of the driving frequency on argon discharge characteristics. These experimental data further improve the precise control of atmospheric pressure discharge parameters.4. Basing on this dual-power electrode structure device, a new-type glow-like discharge device is designed, which is also equipped with two power electrodes as well as a grounded ring electrode near the nozzle exit. The glow-like argon plasma jet is also characterized by means of electrical and spectroscopic diagnosis. It also shows that the root mean square value of conducting current, the average discharge absorbed power, the excitation temperature and gas temperature increase with the applied voltage. However, these parameters decrease with argon gas flow rate. At last, the preliminary study on the surface modification of Polyethylene (PE) Film by using this cold plasma jet is carried out. The experimental results show that the water contact angle of PE Film after treatment decreases obviously (decreasing from 92.55°to 35.55°), which demonstrates that the hydrophily of PE Film is enhanced greatly.5. An atmospheric pressure plasma jet generated by sinusoidal power input of tens of kHz and designed with a concentric wire-mesh cylinder electrode is characterized. Effects of argon flow rate on the length of plasma jet have been investigated, and the plasma jet is seen to have three different modes varied with the gas flow. The jet temperature is measured by fine structure fitting of the emission bands of UV OH, N2 molecules and the Boltzmann plot method, and in comparison with data obtained by optical fiber thermometer. Besides, plasma bullets properties such as velocity, luminosity, their time of formation and extinguishment, and traveling distance are studied with variation of the applied voltage, gas flow rate, and operating frequency of power supply. Results show that the plasma jet is not a continuous volume but a sequence of fast moving bullets at a velocity of 103-104 m/s, much lower than those (104-105 m/s) reported previously. Notably, the bullet velocity is found decreased with the applied voltage but increased with the operating frequency. Furthermore, the maximum velocity is reached earlier for lower gas flow rates and higher applied voltages, while however its value is independent of the gas flow rate.6. A cold atmospheric plasma (CAP) jet array is generated by a two-dimensional (2D) array device of seven CAP jets arranged in a honeycomb configuration and designed with single-electrode configuration as the elemental plasma jet. The discharge characteristics of the plasma jet array are investigated based on detailed electrical, spectroscopic, and imaging characterization. The CAP jet array is shown to achieve good jet-jet uniformity both in time and space. Furthermore, the dynamic behavior of the jet discharges is studied especially through two series of ICCD images taken at the end views. It has been found that the seven jets show a good temporal synchronization and jet-jet uniformity, as well as rich dynamics of jet-jet interactions such as a slight repulsion at surrounding jet heads, especially for small gas flow rate of Helium. These dynamic features offer possible insights with which to better control jet-jet interactions and further optimize the design of large-scale CAP sources.
|
PDF Full Text Request