Temperature Characteristics And Pattern Transitions Of Atmospheric Microplasma

Atmospheric microplasma is one of the research hotspots in the area of plasma.Presenting the clear advantages of being vacuum free,clean,environment friendly and highly effective technology,atmospheric pressure microplasmas have been widely used in plasma biomedical technologies and medicine,nanoparticle synthesis,water purification,plasma agriculture,and some others.In consequence,it is necessary to do research on the effects of different parameters on atmospheric microplasma and the microplasma mechanism in order to make full use of its advantages.In this thesis,a DC discharge system is used to generate atmospheric microplasma and its characteristics are studied by experimental methods.The main works completed in the thesis include two parts.In the first part,the nitrogen rotational and vibriational temperatures under different conditions are measured,and non-equilibrium state of microplasma is studied.It is found that when the discharge current increases,the vibriational temperature of N₂ decreases,the rotational temperature increases,and the system tends to shift more towards the equilibrium state.Under the same discharge conditions,He discharge and He-Ar mixed gas discharge lead to different nitrogen rotational and vibriational temperatures.The variations in the said parameters could be attributed to different thermal conductivities and masses of particles of He and Ar gases.When the gas flux increases,the vibriational temperature of N₂ increases,the rotational temperature decreases,and the system tends to shift more towards the non-equilbrium state.The second part of this thesis is pattern transition of microplasma.Firstly,patterns are observed when the water acts as cathode and anode respectively.The results show that with increasing current the pattern transfers from homogeneous spot to ring-like structure to distinct spots when the water acts as anode,while the transition isn't observed when the water acts as cathode.Secondly,the effects of water temperature and gas composition on patterns are studied when water acts as anode,and it is found that structure of pattern is affected by them.At last,the patterns on the liquid electrode under different conditions are observed,and the corresponding gas temperature of microplasma and temperatures of electrodes are measured.It is observed that the discharge time,discharge gap width,current and gas flux all influence the pattern transitions as well as the gas temperature of the plasma and the temperature of the electrodes.The results show that on the liquid surface the homogenous pattern can only exist at the relatively low gas temperature and electrode temperature.As the gas temperature and the electrodes temperatures rise,the appearances of patterns can change to ring-like structure,distinct spots and gearwheel shape.