Influence of water vapor concentration on discharge dynamics and reaction products of underwater discharge within a He/H2O-filled bubble at atmospheric pressure

In this study,a two-dimensional fluid model is proposed to simulate the underwater discharge in a He/H2O-filled bubble at atmospheric pressure.The molar fraction of water vapor is varied in the range of 0.01%-1%to investigate the dependence of discharge dynamics and reaction products on water vapor concentration(WVC).The numerical results show that most properties of the discharge sensitively depend on the WVC.The increase of WVC leads to an increase in the electron density and discharge propagation velocity,which is attributed to Penning ionization between He*and H2O.The main positive ion switches from He+to H2O+,while the WVC increases from 0.01%to 1%.The dominant reactive oxygen species is OH,whose peak density is about two orders of magnitude higher than that of O.Besides,the densities of OH and O radicals increase with the increasing WVC.It is shown that the formation mechanism of O radicals is significantly affected by the WVC.The dominant reaction creating O radicals changes from the charge exchange between He2+and H2O to the electron impact dissociation of H2O as the WVC increases from 0.01%to 1%.This study is helpful for better understanding the application of non-thermal plasmas discharges in water,such as biomedical,environmental engineering.

Numerical study on an atmospheric pressure helium discharge propagating in a dielectric tube:influence of tube diameter

In this work, a two-dimensional numerical simulation of the discharge characteristics of helium plasma propagating inside a dielectric tube was performed. A trapezoidal ＋9 kV pulse lasting 400 ns was applied on a needle electrode set inside the dielectric tube to ignite the discharge. The discharges generated in the tubes with a variable or a constant inner diameter were investigated.The focus of this study was on clarifying the effect of the tube diameter on the discharge structure and dynamics. The comparison of the discharge characteristics generated in dielectric tubes with different diameters was carried out. It was shown that the tube diameter plays a significant role in discharge behavior of plasma propagating in the dielectric tube.

Dynamics of ionisation wave propagation in an applied external electric field

This study presents spatio-temporal development of the ionisation waves(IWs)along one dielectric tube with an extra alternating electric field.A pulsed direct current power supply is used for generating the IWs,and another alternating current power supply is used for altering the distribution of electric fields along the dielectric tube.The measurements show that the propagation velocity and density of IWs are strongly affected by the external electric field.The direct relation between external electric field and the velocity of the IWs is demonstrated.Further analysis indicates that the external electric field can be utilised to control the propagation of the IWs,resulting in a change of their density and velocity.