Spatio-Temporally Resolved Target Electric Field Measurements In Atmospheric Pressure Plasma Jet Based On Pockels Effect

Atmospheric pressure plasma jets(APPJs)have shown great application value in the fields of biomedicine,materials science,agriculture,and environmental protection.The APPJs can be easily generated and does not need any equipment to control or maintain the pressure.The APPJs is generated with a strong electric field,and the electric field plays a crucial role in the treated sample.Therefore,when the APPJ interacts with the sample,the quantitative description of the electric field distributed on the sample will be helpful to explain the relevant scientific issues in the interaction between the APPJ and the treated sample.In this thesis,helium is the working gas of the APPJ,sine wave AC high-voltage power source is used as the power source,and the APPJ is generated at atmospheric pressure.Spatio-temporally resolved polarization imaging technology based on the Pockels effect of BSO(Bi₁₂Si O₂₀)crystal is combined with the electrical measurement are used in this study.The distribution of the target electric field induced by the APPJ is established by changing the electrical parameters and gas flow rate of the APPJ.The main research results obtained are as follows:A pin-ring structure APPJ is used to generate the discharge plasma,by changing the electrical parameters of APPJ,the spatio-temporally resolved target electric field was studied.The measurements show that when APPJs impinging on the surface of BSO crystal,the change of the electric field can be divided into the establishment phase,the continuous phase of the electric field near the APPJ nozzle,and the“erasing”and extension of the electric field;When the peak-to-peak applied voltage(V_PP)increases from 5.4 kV to 8.2 kV,the peak electric field detected on the crystal surface gradually increases.The initial electric field value increases from about 3 kV/cm to about 5.5 kV/cm,and the peak electric field increases from about 4.5 kV/cm.to 8.5 kV/cm.In addition,the increase in discharge area and electric field leads to an increase in total charge deposition from about 4 nC to about 22 nC;when the voltage frequency increases from 4 kHz to 12 kHz,the initial electric field value increases from about 2.3 kV/cm to about 4.3 kV/cm.The peak value of the electric field increased from about 5 kV/cm to 7.5 kV/cm.At the same time,the peak value of the total charge in the voltage cycle increased from about 6 nC to about 13.5 nC.According to the analysis of the experimental results,it is believed that the increase of the applied voltage will increase the electron energy in the discharge process,and the avalanche effect of the discharge;in addition,the increase of the frequency will accelerate the voltage rising and falling rate,reduce the discharge interval,and increase the background electron density.The increase in discharge intensity is the main reason for the increase in the electric field on the surface of BSO.By changing the helium flow rate,the influence of the gas flow rate on the temporal and spatial distribution of the target electric field of APPJ is studied.The experiment found that as the gas flow rate increases from 200 sccm to 1000 sccm,the maximum electric field value formed by the deposited charges on the crystal surface first increases and then decreases.When the gas flow rate increases from 400 sccm to 1000 sccm,the initial electric field value decreases from about 3.5 kV/cm to about 3 kV/cm,and the electric field peak value decreases from about 7.5 kV/cm to 6 kV/cm.It is believed that the decrease of the electric field intensity may be related to the mixing of air at a lower gas flow rate,and the increase in Penning effect caused by air diffusion is the possible reason of the increase in field strength.In addition,the total deposited charge is also related to the gas flow,and the discharge area increases with the increase of the gas flow,resulting in a gradual increase in the total deposited charge.