Characteristics Of DC Corona Discharge And Its Spatial Ions Behaviours

DC corona discharge is one of the typical forms of gas discharge at high pressures.It has been prosperously thriving in ion source,electrostatic detection,flow control,thermal cooling,surface treatment and environment engineering due to its easy operation,lower inception voltage,lower gas temperature and large range of gas pressure,etc.The research on ions behaviors during corona discharge benefits in a better understanding of discharge mechanisms and has guiding significance in its practical applications.In this thesis,the spatial-temporal behavior of ions is investigated experimentally and numerically,especially in Trichel pulse of negative corona and ionic wind process.The thesis includes three parts as follows:Firstly,the characteristics of Trichel pulse in negative corona discharge are investigated experimentally.The effect of averaged current,gap spacing,tip curvature radius of cathode and gas pressure on the pulsed current has been examined respectively.The spatial-temporal development of discharge during the pulse is analyzed by optical analysis and time-resolved images.It is found that the formation of Trichel pulse correponds to the periodical accumulation of positive ions and hence the enhancement on local electric field.It is experimentally evidenced that Trichel pulse exists not only in electron-negative gases but also in non-electron-negative gases.The pulse characterristics are determined by the physical process only around the cathode,not depending directly on the electrode gap or the applied voltage.Trichel pulse has similar features with the self-pulsing in other systems like hollow cathode discharges and parallel-plate discharges that the pulsing is actually a mode transition between Townsend and glow modes.Secondly,the ionic wind produced by corona discharge is investigated under both negative and positive polarities.The characteristics,including wind velocity,wind distribution and active range as well as the influence of discharge parameters,are tested.A physical model is established and the wind velocity is theoretically deduced.Based on the discharge mechanisms and ions behavior in space,a qualitative discussion is made.It is shown that the distributions of ions and electric field are crucial factors for the ionic wind.The wind velocity is determined by the over-voltage.Due to the difference of discharge mechanisms,the positive ionic wind has a larger velocity,but the negative ionic wind has a wider active range.Finally,a two-dimensional fluid model is established,which can simulate the Trichel pulse and ionic wind processes of corona discharge.The spatial-temporal behavior of ions is investigated numerically.The results show that positive ions have the crucial effect on the pulse formation,while the negative ions have some influence on the pulse decay and interval.During the rise time of pulse,positive ions accumulate in front of the cathode,forming the cathode sheath and inducing the glow breakdown.The pulse decay corresponds to the destruction process of the ion sheath,which can be accelerated by the negative ions.During the pulse interval,the negative ions dissipate gradually and the positive ions re-accumulate.Besides,the ionic wind is produced by the directional movement of particles,which is driven by the drift of ions.The ionic wind process is mainly determined by the behavior and distribution of spatial ions.In negative corona,negative ions exist in a lager area of the gap spacing and its drift leads to wider-range of ionic wind.In positive corona,the positive ions always accumulate in front of the discharge channel,promoting the discharge development and inducing a smaller-range of the ionic wind.But the positive ionic wind has a larger velocity than the negative wind.