Numerical Investigation On The Behavior Of Electrons In The Bullet In The Atmospheric-Pressure Ar/O₂ And He/O₂ Plasma Jets

Atmospheric-pressure low-temperature plasma jets have been extensively used in biomedical field.It has been well shown that when the biological tissue is irradiated using the plasma jets,the expected biomedical effects occur mainly through the interaction of the reactive substance with the biological tissue.The plasma jets can produce various reactive species.In the mass transfer of the plasma jet in aqueous solution,electrons play an important and active role in participating in the synergistic interaction between reactive species.Due to the above,it is of significance to have a deep and systematic understanding of the behavior of electrons in the plasma jet.In this thesis,based on a needle-plate discharge configuration and a one-dimensional particle-in-cell Monte-Carlo collision(PIC-MCC)method,the parameter effects and corresponding mechanisms of electron behavior in the bullet in the atmospheric-pressure low-temperature plasma jets have been studied numerically.This thesis includes the following contents and results:1.A systematic investigation has been carried out on the behavior of the electrons in the bullet in the Ar/O2 plasma jets in changing oxygen concentration and the amplitude of the applied voltage,including the energy and angle spectra of electrons,the electron density,the generation of reactive species,and the ratio of energetic electrons to all the electrons in the bullet.The correlation is also probed between the electron density and the generation of reactive species.The main conclusions are obtained as follows:(1)The increase in oxygen concentration allows more electrons to be scattered towards the target,i.e.,more electrons to most probably interact with the target,and induces a dramatic increase of reactive species,but leads to the decrease of the bullet velocity and average electron energy.In addition,there is only a weak correlation between the electron density and the generation of three important reactive species,O(1D),O-,and O2(a1Δg).(2)Increasing the applied voltage,the electrons scattered towards the target decreases,in spite of this,the majority of these electrons,above 70%,are of energy higher than 3.27 eV,an energy threshold of inducing a dissociative electron attachment to water molecule.These are beneficial to the generation of reactive species in the mass transfer of the plasma jet in aqueous solution.In addition,there is a strong correlation between the electron density and the generation of O(1D),O-,and O2(a1Δg).(3)The increase of reactive species with oxygen concentration is large in comparison with that with the applied voltage,thus showing that to increase the addition of O2 to Ar can significantly promote the generation of reactive species.2.A comparative investigation has been done on the oxygen concentration effects of electron energy spectrum,electron angle spectrum,high energy electron,and reactive species in the bullet in the Ar/O2 and He/O2 plasma jets.The main conclusions are obtained as follows.(1)At a fixed oxygen concentration,compared with Ar/O2,the peak value of electron energy spectrum in the He/O2 plasma jet is low and the distribution range is wide.With the increase of oxygen concentration,although the average electron energies in both Ar/O2 and He/O2 plasma jets gradually decrease,the average electron energy in He/O2 is significantly higher than that in Ar/O2.Furthermore,the peak position of electron angle spectrum gradually shifts towards small angle in the He/O2 plasma jet,meaning more electrons scattered towards the target.(2)The proportion of electrons with energy higher than 3.27 eV in the angle range of θ<90° in the Ar/O2 and He/O2 plasma jets is above 70%.The density of reactive species in the bullet in the Ar/O2 plasma jet is higher than that in the He/O2.