水中脉冲电压放电形成等离子体通道模拟分析

Formation and Growth of Plasma Channels Generated by Discharge of High Voltage Nanosecond Pulse in Water: A Simulation Study

为获得水中纳秒脉冲电压下放电形成等离子体通道的发展过程,建立水中放电流体模型的数学方程,利用COMSOL软件的有限元方法求解二维轴对称情况,模拟出针-板电极之间的电场强度、电子密度、氢离子密度以及氢氧根离子密度等随时间和空间的分布,并研究脉冲电压幅值、电极间距、电导率对这些物理量以及流注形貌的影响。模拟结果表明:针电极尖端的高场强使高纯水产生最初的电离,之后产生的空间电荷进一步加强了流注头部场强,使流注头部向前推进,形成等离子体通道;当针-板电极间距较小和所加脉冲电压幅值相对较低时,电极间只形成单流注通道,且通道内的电场强度与电子密度随着电压幅值的略微升高而增大,呈线性变化;当所加脉冲电压的幅值高到一定程度时,单流注通道出现"分叉",通道内的电子密度随电压幅值的变化不再是线性的。当针-板电极间距较大时,反应腔内则形成类似于"树枝"状的等离子体通道。当用电导率较高的自来水替代高纯水作为反应介质时,流注头部场强与等离子体通道内的电子密度明显提高。

The formation and growth of plasma channel(s),generated by discharge of high voltage nanosecond pulse in water,was empirically approximated,mathematically modeled,theoretically analyzed,numerically simulated with COMSOL and experimentally evaluated with the lab-built setup.The influence of the properties of voltage pulse and water conductivity on the time evolution of the plasma characteristics,including the distributions of ion/electron densities,shape of plasma channels,was investigated.The results show that depending on the voltage,the field ionization zone,above the tip-apex where the strongest field exists,has a major impact.For example,at a less high voltage,single ion-beam,forming in ionization zone,moves forward increasingly faster,accompanied by strong collision ionization of water molecules,consequently,a plasma channel appeared;at a high voltage,splitting of plasma channel occurs and the possible mechanism were tentatively discussed.De-ionized water increased the e-density of plasma channel and field at its front.