Time-resolved Diagnosis Of Micro Plasma At Atmospheric Pressure

Atmospheric pressure microplasma jet has the characteristics of high electron density and low gas temperature,and has a wide application prospect in the fields of biomedicine and material processing.In order to further study the discharge process of microplasma jet,it is necessary to know the variation of each characteristic physical quantity with time,which is helpful to guide the research and development of microplasma generator.Therefore,in this paper,a single-tube microplasma with a diameter of 4 m and a single-hole microplasma array with an inner diameter of 200 m are taken as the research objects to carry out nanosecond high-resolution diagnosis of electron density,temperature,charge and other characteristics.Using nanosecond pulse discharge,an argon microplasma jet with a length of 2.7cm was generated in a capillary tube with a diameter of 4 cm.The dynamic process was photographed with an ICCD camera with an exposure time of 3 ns,and it was found that 4 process of discharge occurred within the monopulse,which was closely related to the output oscillation waveform of the power supply.The influence of power voltage amplitude,frequency and working gas on jet velocity and propagation distance is studied.It is found that power frequency has the greatest influence on jet velocity and propagation distance.Where,the jet velocity is 1×10⁶ m/s?4×10⁶ m/s.The electron density was measured by means of the stark expansion of the h-line and the ar-line by the high-time-resolved radiation spectroscopy.The maximum electron density was 33.1×10¹⁶/cm3,which was 3?5 orders of magnitude higher than that of the mm-class jet.Through the simulation of Comsol software,the electric field intensity of the electrode front reaches 10¹⁰ V/m.Using nanosecond pulse discharge,a helium microplasma array jet is generated in an array tube with a single hole diameter of200 nm.The effects of three different electrodes on the length and uniformity of the jet were compared.It was found that the needle-DBD electrode device with flat electrode produced ideal uniformity and length of the jet,which could achieve uniform discharge of 5 jet tubes with an average length of 3 cm.The dynamic propagation image of discharge with 3 ns time resolution was obtained by ICCD camera,and the influence of power supply voltage and working gas composition on the propagation velocity and propagation distance of the jet array was studied.It was found that the jet velocity was(0.5?4)×10⁶ m/s.The maximum electron density was 33.7×10¹⁴/cm3 through stark broadening of the H 486.1 nm spectral line,and the electron density rapidly decreased to about10×10¹⁴/cm3 with discharge.The gas temperature and vibration temperature of the microplasma array change with time through the measurement and fitting of nitrogen molecular spectra.It was found that the gas temperature was maintained at 400 K?500 K,the vibration temperature varied widely with time,and the array jet temperature had a cumulative effect,reaching a maximum value of3200 K at 60 ns of the second discharge process.