【作者】 张宇；

【导师】 欧阳吉庭；

【作者基本信息】 北京理工大学 ， 凝聚态物理， 2016， 博士

【摘要】 直流电晕放电是一种常见的高电压气体放电形式,具有放电结构简单、放电电压低、气体温度低、气压范围宽等优势,广泛应用于离子源、静电探测、气流动力学改性、微区散热、表面处理以及环境工程等领域。对放电过程中离子行为的探讨,有助于加深对直流电晕放电机理的认知,并对实际应用有着重要的指导意义。本文从实验和数值模拟两个方面对直流电晕放电中的离子空间行为开展研究,详细考察了负电晕放电Trichel脉冲、电晕离子风现象中的离子微观过程。全文分为三部分:首先,实验研究了负电晕放电Trichel脉冲的基本特性,探究了放电平均电流、电极间距、阴极曲率半径、环境气压等条件对脉冲特性的影响,并结合光谱诊断与时空分辨图像,探讨了Trichel脉冲放电的时空发展过程。发现Trichel脉冲现象源于正离子的空间聚集及其对电场的畸化加强,既可以在电负性气体中发生,也可以在非电负性气体等其他气体中发生。脉冲特性仅与阴极附近的状态和物理过程有关,与电极间距、放电电压等并不直接相关。Trichel脉冲与空心阴极、平行板电极等放电结构中的自脉冲过程相似,都是Townsend放电和辉光放电之间的模式转换。其次,实验研究了不同极性直流电晕放电离子风的特性,考察了过电压、电极间距、阴极曲率半径等条件对离子风风速、风区分布和有效作用半径的影响。建立了直流电晕离子风的电流体近似模型,从离子空间行为出发对离子风速进行了理论推导,并结合正、负电晕放电机制,分析了非均匀电场下的电晕放电发展与电流体行为,对离子风的形成及其特性进行了定性解释。发现空间电场与离子的分布形式是离子风的主导因素,其最大风速由电晕放电过电压决定。由于放电机制差异,正电晕离子风的风速更大,但负电晕离子风的有效作用面积更广。最后,建立了直流电晕放电的二维流体模型,着重考察了放电过程中空间离子的微观行为,对负电晕Trichel脉冲、电晕离子风现象进行了仿真与重现。发现负电晕Trichel脉冲是正离子聚集与消散交替进行的微观过程,负离子可以对离子鞘消散过程起到一定作用。脉冲上升沿中,正离子在阴极附近积累、形成离子鞘层并引发瞬态辉光击穿和放电。脉冲下降沿对应于正离子鞘的消散和破坏,负离子的存在将加速这一过程。脉冲间隔则是负离子清除与正离子重新积累的过程。电晕放电的离子风则是放电空间离子在电场作用下迁移引起的宏观定向粒子流,主要由空间离子行为和分布决定。负电晕中负离子存在空间范围较大,其迁移运动带动中性气体分子从而产生m/s量级的离子风。正电晕中正离子总是位于放电发展通道的前端较小区域,推动放电发展并引发离子风;其风速比负离子风略高,但有效半径偏小。更多还原

【Abstract】 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.更多还原