Study Of Influence Of Different Gas Ambient On Characteristics Of Atmospheric Pressure Helium Plasma Jet

Atmospheric pressure plasma jet(APPJ)has broad application prospect in the fields of materials processing,nanosynthesis,environmental engineering,biomedicine and so on.APPJ has gradually become one of the hot topics in the field of atmospheric non-equilibrium plasma in recent years.APPJ need to be maintained and developed in open spaces,and it is bound to cause the plasma jet working gas and the environment gas blending.This will influence the plasma jet characteristics.For this problem,this paper studies the effects of ambient gases such as air,nitrogen,argon and helium on atmospheric pressure He plasma jets by using CCD imaging,electrical measurement,optical emission spectroscopy and other methods.The effects of different gas ambient on jet shape,electrical characteristics and discharge products of atmospheric pressure He plasma jet were compared.The result is as follows:1.Ambient gases can participate in the development of atmospheric pressure plasma jets and affect the plasma jet characteristics.The ambient gas with low excitation and ionization energy can rapidly consume high-energy particles in the jet,which will shorten the jet propagation distance.The ambient gas with high excitation and ionization energy is more difficult to consume high-energy particles,and the jet spread further.In the experiment of this paper,the length of the helium plasma jet is argon ambient>nitrogen ambient>helium ambient>air ambient.The excitation and ionization energy of the ambient gas can affect the number of high-energy electrons in plasma jet that can excite the low-energy He atoms to He(33S1).There are fewer such high-energy electrons inside plasma jet in ambient gas with high excitation and ionization energy,and lines of He(33S1?23P0,1,2)706.5 nm is weak.The excitation and ionization energy of ambient gases play a decisive role in the propagation of plasma jet.2.In the same gas ambient,the length of helium plasma jet is influenced by the discharge parameters which include excitation voltage,working gas flow and so on.The length of plasma jet can be controlled by changing the excitation voltage and the helium flow.When the effective value of the excitation voltage is increased between 2.5 and 5.5 kV,the length of the needle-ring electrodes helium plasma jet is increased to 25 mm and then decreases.When the helium flow is increased between 1.0 and 3.0 L/min,the length of the ring-ring electrodes helium plasma jet is increased to 33mm.In four ambient gases(air,nitrogen,argon,helium),the electrical characteristics of the helium plasma jet are not very different.With the increase of the excitation voltage,the phase of current main pulse is advanced,and the amplitude of pulse decline,and the number of micro-discharge pulses increased significantly.In different gas ambient,the increase of the flow rate of the working gas(helium)can enhance the discharge stability and inhibit the generation of micro-discharge.The transmission charge and the discharge power of helium plasma jet are basically consistent with the increase of voltage in four ambient gases.3.The optical emission spectrum of atmospheric pressure helium plasma jet is different in different gas ambient.There are four He lines(587.5,667.8,706.5,728.1 nm),and the lines of N2(C3?u-B3?g)? N2+(B2?u+-X2?g+)are much and strong in air and nitrogen ambient.There is a line of 0(777.5 nm)in air ambient,and there is a line of OH(309 nm)in nitrogen ambient.The nitrogen molecular lines are very weak and there is only one N2+ line in argon ambient.In argon ambient,there is a large number of Ar(4p-4s)spectral lines,and the OH line is stronger than nitrogen.In helium ambient,there are only lines of N2,N+2 and He,and these lines are weak.4.The electron excitation temperature is calculated by using spectral data and the molecular rotational temperature is fitted.The electron excitation temperature is between 0.14 and 0.16 eV which is calculated by He lines,and there is little change with the increase of excitation voltage in air and nitrogen ambient.The electron excitation temperature is between 0.64?1.37 eV which is calculated by Ar lines,and it becomes larger with the increase of excitation voltage in argon ambient.The results of the molecular rotational temperature fitting of atmospheric pressure helium plasma jet are 389 K(air),380 K(nitrogen),335 K(argon)and 436 K(helium).