| In recent years,atmospheric pressure non-equilibrium plasma jets have been widely used in biomedical field,such as sterilization,cancer treatment,skin treatment,root canal treatment and so on.In order to develop a plasma jet source for biomedical applications,the paper studies an atmospheric pressure mm-size plasma jet which is driven by DC and the atmospheric pressure?m-size plasma jet.First of all,with a floating needle?positive polarity?-to-ring?negative polarity?electrode configuration insulated by the quartz tube,an atmospheric-pressure helium plasma jet driven by bipolar dc voltage is demonstrated.It is found that the current of plasma jet is in the form of pulse,whose pulse repetition frequency is 0.8-2 kHz,which can be safely touched by human body without feeling electric shock or thermal damage.The effects of electrode position,gas flow rate and electrode structure on the plasma jet were studied to determine the best discharge parameters.Secondly,In order to study the characteristics of the microplasma,the diameter of the tube is reduced.An atmospheric-pressure microplasma plume of diameter 10?m is generated inside a long tube.The length of the microplasma plume reaches as much as 2 cm.First,with the assistance of an air dielectric barrier discharge?DBD?,the ignition voltage of the microplasma decreases from 40 kV to23.6 kV.Second,although the current density reaches as high as?1.2-7.6?×104 cm-2,comparable to the current density in transient spark discharge,the microplasma plume is non-thermal.Third,the electron density measured by the Stark broadening of Ar spectral line 696.5 nm reaches as high as 3×1016 cm-3,which is 2-4 times higher than the mm-sized plasma jet.In addition,the propagation velocity of the microplasma plume,obtained from light signals at different axial positions,ranges from 1×105 m/s to5×105 m/s.At last,in order to study the effect of tube diameter variation on the microplasma jet,capillaries in the range of 4-100?m were selected.When the tube diameter decreases,the length-diameter ratio,the ignition voltage,the current density,and the electron density increases significantly.For the tube diameter of 9?m,the electron density measured from Stark broadening of H?line reaches 11×1016 cm-3.Detail analysis shows that the diffusion or drift loss of electrons and Ar metastables may play a dominant role in the high ignition voltage and high electron density. |
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