arXiv 1310.43072013-10physics.plasm-ph

用双脉冲实验研究正流光，重复频率和气体的影响

Investigation of positive streamers by double pulse experiments, effects of repetition rate and gas

S. Nijdam, E. Takahashi, A. H. Markosyan, U. Ebert

备注：: 27 pages, 17 figures
DOI：: 10.1088/0963-0252/23/2/025008

摘要：

流光放电通常以重复脉冲模式操作，并且因此受到从先前放电留下的物质的影响，特别是自由电子和离子。我们已经研究了这些影响，通过施加两个连续的正高压脉冲的持续时间为200-700 ns的点平面间隙在人工空气，纯氮，其他氮-氧混合物和纯氩在67和533毫巴之间的压力。脉冲的脉冲间间隔（Δt）在200 ns和40 ms之间。我们用两台ICCD相机对两种放电进行成像，并将其组合成复合图像。我们观察到Δt值低于0.5-15 μs（在133毫巴，取决于气体混合物），在第二个脉冲期间，流光继续第一个脉冲流光的路径。我们把这种延续仍然发生的最大时间称为延续时间。对于N $_{2}$ - O $_{2}$混合物，该时间在约0.2%的氧浓度下具有最大值。根据我们的等离子体化学建模，该最大值由电子损失率确定，该电子损失率在该氧浓度附近具有最小值。取决于氧浓度，主要的重组正离子是N $_{4}^{+}$、O $_2^+$或O $_{4}^{+}$，其中O $_{2}^{+}$在O $_{2}$的0.2%左右占主导地位，并且重组最慢。随着Δt值的增加，我们观察到，在延续阶段之后，首先根本没有新的流光出现，然后新的流光出现，避开了整个预电离区。接下来，我们看到新的薄飘带沿着旧通道的边缘。对于较大的Δt（10-200 μs），新的拖缆的尺寸开始增加，并移动到旧通道的中心。最后，在毫秒时间尺度附近，新通道完全独立于旧通道。

英文摘要：

Streamer discharges are often operated in a repetitively pulsed mode and are therefore influenced by species left over from the previous discharge, especially free electrons and ions. We have investigated these effects by applying two consecutive positive high voltage pulses of 200-700 ns duration to a point plane gap in artificial air, pure nitrogen, other nitrogen-oxygen mixtures and pure argon at pressures between 67 and 533 mbar. The pulses had pulse-to-pulse intervals (Δt) between 200 ns and 40 ms. We imaged both discharges with two ICCD cameras and combined this to a compound image. We observe for values of Δt below 0.5-15 μs (at 133 mbar, depending on gas mixture) that during the second pulse the streamers continue the paths of the first-pulse streamers. We call the maximal time for which this continuation still occurs the continuation time. For N$_{2}$ - O$_{2}$ mixtures, this time has a maximum at an oxygen concentration of about 0.2%. According to our plasma chemical modelling this maximum is determined by the electron loss rate which has a minimum around this oxygen concentration. Depending on oxygen concentration the dominant recombining positive ion is N$_{4}^{+}$, O$_2^+$ or O$_{4}^{+}$ where O$_{2}^{+}$ dominates around 0.2% O$_{2}$ and recombines slowest. For increasing values of Δt we observe that after the continuation phase first no new streamers occur at all, then new streamers show up that avoid the entire pre-ionized region. Next we see new thin streamers that follow the edges of the old channels. For larger Δt (10-200 μs) the new streamers start to increase in size and move to the centre of the old channel. Finally, around millisecond timescales the new channels are completely independent of the old channels.

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英文摘要：

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