Experimental And Numerical Investigation On Slender Plasma Excited By Low Frequency Discharge

The characteristics of plasma source depend not only on the way of generation but also on the shape,structure and materials of electrode and so on.On the other hand,due to their special shapes,it is relatively difficult to diagnose non-conventional plasma sources applied in different plasma processing.However,understanding the discharge mechanism of a plasma source plays an important part in optimizing its design and developing its potential application.In this paper,we generate cold slender plasma and microplasma sources in a wide range of gas pressure.The characteristics of slender plasma in low gas pressure are investigated by experiment and simulation,and two types of cold plasma sources including microplasma jet and slender plasma jet in atmospheric pressure are developed.At last,preliminary study of application of these non-conventional plasma sources is discussed.For the special discharge shape of cold slender plasma source in low pressure,it remains some difficulty in the diagnosis of its characteristics.Up to now,to our knowledge,there are few papers related to discharge mechanism of cold slender plasma source can be found.In this paper,a slender cold Ar plasma is excited in low frequency in configuration of two parallel cylinder electrodes under low pressure of 50 Pa,and the plasma features are characterized using an asymmetric double probe.It is found that the electron energy distribution function significantly devitates from the Maxwellian in 10KHz,and Electrons in the regions near the power electrode possess a higher temperature and density compared with the other two regions.As the discharge voltage is enhanced,both electron temperature and density increase quickly near the power electrode.Because changing of discharge frequency in the experiment does not affect the discharge mechanism,the electron temperature and density in various locations remain unchanged.The electron temperature increases obviously when the power electrode is covered by a glass tube.Only when the content of hydrogen reaches a certain proportion,the electron temperature increases obviously,and density decreases quickly with the enhancement of proportion of hydrogen in the argon discharge.The results of probe diagnosis are consistent with that of optical emission spectroscope(OES).A two-dimensional,self-consistent fluid model combined with Monte Carlo simulation is employed to describe the cold slender plasma.The electron temperature, electron density and discharge current are calculated,and compared favourably with experimental data.The calculation of electric field presents a spatiotemporally asymmetrical distribution,which results in the difference of distribution of electron temperature and density near the two electrodes.With the increasing in the size of power electrode,the ionization rate of gas near two electrodes becomes symmetric gradually.The SiO_x films grown on PET substrates by cold slender plasma in low pressure contain relatively little organic materials,and the surfaces of the SiO_x films are smooth without any large particles.Changing raw material gas(HMDSO) content has little effect on the quality of SiO_x films.A cold microplasma jet generator at atmospheric pressure excited at 1 kHz in a pin to hole-electrode configuration by using soft materials partly is development.A nitrogen plasma plume with a length of more than 5 cm can be produced at low electrical power of 0.7 W without high feed gas pressure.The generator exhibits a compact structure with flexible property,which is suitable for treating thermally sensitive materials and biomedical materials,especially for delicate objects in an irregular confined space.Optical emission spectroscopy is used to spatially identify excited species in plasma plume.It is noted that the spectrum intensities of all the excited species decay quickly.A cold slender plasma jet generator at atmospheric pressure excited at 10 kHz is developed based on microplasma jet generator.The nitrogen plasma jet is stable and uniform at low electrical power of 19 W with a horizontal length of 32mm.For using suspended electrodes,the electric power can be adjusted conveniently without causing spatial nonuniformity.The slender plasma jet with room gas temperature can be touched by human skin,and is suitable for treating the surface of polyethylene(PE), polypropylene(OPP),biaxial oriented polypropylene(BOPP),paper and glass. Compared with slender DBD,slender plasma jet is not restricted by the morphology of surface,and causes little damage to targets.