Investigation of discharge mechanisms in helium plasma jet at atmospheric pressure by laser spectroscopic measurements
Investigation of discharge mechanisms in helium plasma jet at atmospheric pressure by laser spectroscopic measurements
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DOI：
10.1088/0022-3727/43/9/095201
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发表时间：
2010-03-10
影响因子：
3.4
通讯作者：
Ganguly, Biswa N.
中科院分区：
文献类型：
--
作者：
Urabe, Keiichiro;Morita, Tadasuke;Ganguly, Biswa N.
我们用激光光谱方法测量了等离子体喷流中激发态的时空结构，等离子体喷流由重复率为千赫兹量级的双极脉冲电压脉冲串驱动，穿过包裹着氦气的玻璃管的一对电极。我们注意到，当背面电极接地时，施加到靠近管子出口的前端电极的电压的正相和负相之间的差异。实验结果表明，激发态物种的径向分布在正电压相呈中空分布，而在负电压相分布较为均匀。正相中氦亚稳原子的峰密度几乎是恒定的，与峰值电压无关。但在负相时，随着峰值电压的增加而增大。从正负电晕放电两个方面论证了产生这些差异的机理。我们还研究了在类似于材料加工的条件下，在等离子体喷嘴前面放置导电衬底的等离子体羽流的性质。在这种情况下，电子碰撞电离产生的等离子体在衬底附近占主导地位，这从氦亚稳原子和氮离子密度的时空分布中可以看出。
We have measured spatiotemporal structures of excited species by laser spectroscopic methods in a plasma jet, which was driven by a bipolar impulse voltage pulse train of the order of kilohertz repetition rate applied across a pair of electrodes wrapped around a glass tube with a helium gas flow. We noticed the differences between the positive and the negative phases of the voltage applied to the front-side electrode placed closer to the tube exit while the back-side electrode was grounded. The experimental results showed that the radial distribution of the excited species had a hollow shape at the centre in the positive voltage phase, while it had a more uniform shape in the negative phase. The peak density of the helium metastable atom in the positive phase was almost constant irrespective of the peak applied voltage. However, it increased with the increase in the peak applied voltage in the negative phase. The mechanism causing these differences was argued from the respects of positive and negative corona discharges. We have also investigated the property of the plasma plume under conditions similar to material processing with a conductive substrate placed in front of the plasma jet. In this case, the plasma production by electron impact ionization became dominant near the substrate as was revealed from the spatiotemporal distributions of helium metastable atom and nitrogen ion densities.