Mass spectrometric diagnosis of an atmospheric pressure helium microplasma jet
Mass spectrometric diagnosis of an atmospheric pressure helium microplasma jet
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DOI：
10.1088/0022-3727/46/46/464018
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发表时间：
2013-10
期刊：
影响因子：
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通讯作者：
K. McKay;Jun-Seok Oh;James L. Walsh;James W. Bradley
中科院分区：
文献类型：
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作者：
K. McKay;Jun-Seok Oh;James L. Walsh;James W. Bradley
利用环境分子束质谱(MBMS)研究了不同的毛细管宽度(530µm和2.4 mm)和激励波形(连续波kHz和脉冲直流)对大气压等离子体射流离子组成的影响。从时间平均离子强度可以看出，减小喷射毛细管的宽度会显著增加放电中检测到的正负离子种类。我们从流动速度的变化和等离子体羽流中湍流的开始来讨论这一问题。改变激发方式对从微等离子体射流中检测到的离子物种几乎没有影响；但是，当工作在连续波千赫模式时，优势离子显著地向更高质量的离子转移。在工作频率分别为5 kHz和15 kHz的两种激发源下，观察到了微等离子体射流内离子的时间演化。正离子产生在与放电电流正负峰对应的时间段，负离子主要产生在放电电流负峰时。这种现象与驱动波形无关。对于脉冲直流激励，在与负电流峰值相关的周期内产生的正离子相当少，尤其是在较高频率时。基于流光传输和等离子体羽流中自感电场的影响，我们对这些过程提出了一个简单的解释。
Ambient molecular beam mass spectrometry (MBMS) has been used to study how different capillary widths (530 µm and 2.4 mm) and excitation waveforms (continuous wave kHz and pulsed dc) affect the ionic composition of atmospheric pressure plasma jets. It is shown from time-averaged ion intensities that reducing the width of the jet capillary results in a significant increase in the variety of both positive and negative ions detected within the discharge. We discuss this in terms of changes in flow velocity and the onset of turbulence within the plasma plume. Changing the mode of excitation had little effect on the ionic species detected from the microplasma jet; however, there was a notable shift in dominance towards higher mass ions when operated in a continuous wave kHz mode. The temporal evolution of the ions within the microplasma jet was observed for both excitation sources, operated at 5 and 15 kHz. Positive ions were created during periods correlated with the positive and negative peaks in discharge current, while negative ions were predominantly created at times when the discharge current peak was negative. This phenomenon was independent of the driving waveform. For pulsed dc excitation, considerably fewer positive ions were created in periods related to the negative current peaks, especially at higher frequencies. We propose a simple explanation for these processes based on ideas of streamer propagation and the influence of self-induced electric fields in the plasma plume.