大气压纳秒脉冲裸电极放电的粒子模拟研究

PIC-MCC Numerical Study on Discharge Characteristics of Atmospheric Nanosecond-pulse Discharges Without Dielectric Barriers

大气压纳秒脉冲放电由于能量利用率高、可以生成多种活性粒子且容易形成均匀的放电等优势,在等离子体环境、医学等应用方面具有广阔的前景。为此借助于粒子模拟方法,研究了在裸电极条件下,纳秒脉冲放电的演化过程及放电机理。由于电极表面没有覆盖介质,在脉冲电压施加过程中,只能观察到一次放电,放电电流一般在电压下降沿开始时刻附近达到最大值。在电压上升沿及坪区阶段,鞘层电场持续增强,鞘层厚度逐渐变薄,电子能量概率分布函数存在明显的高能尾部,电子与离子数密度可以达到很高的数值;放电的熄灭主要是由于脉冲电压的下降造成的,即使在脉冲电压下降阶段,由于前面阶段放电剧烈鞘层电场非常强,碰撞电离依旧可以持续一定的时间。通过粒子模拟研究脉冲电压驱动的裸电极放电,并与相应的介质阻挡放电比较,有助于深化对纳秒脉冲激励的放电演化过程与内在机理的认识。

We present a theoretical study on the atmospheric plasmas driven by nanosecond-pulse voltages without dielectric barrier covered on the electrodes by using PIC-MCC simulations. The numeric simulation results show that only one discharge event can be observed when the pulsed voltage is applied on the bare electrodes, which displays very different discharge pattern from the case that the electrodes are covered by dielectric barriers. The discharge current density almost reaches the peak value at the moment when the pulse voltage starts to decrease. During the voltage increasing phase, the sheath field keeps increasing and the sheath thickness becomes smaller, and a high energy tail of electron energy distribution function can always be observed, simultaneously, a plenty of electrons with very larger value are also produced. The space charges in the sheath region significantly enhance the electric field. The eventual extinguishment of the discharge occurs in the decreasing phase of applied voltage, but still possesses very strong electric fields in the sheath region. From the simulation data, the discharge evolution and underpinning physics of atmospheric plasmas driven by nanosecond pulsed voltage can be further understood.