大气压等离子体射流可以在开放的空气环境中产生富含多种活性粒子的低温等离子体羽,在材料合成、表面改性、生物医疗、环境保护等多种领域具有广泛的应用前景. 等离子体羽的形貌与活性粒子的时空分布有关,研究其形貌对等离子体射流的应用具有重要意义.针对目前等离子体形貌还不够丰富的问题,本文利用氩气等离子体射流,通过改变外加电压参数(电压峰值、驱动频率和偏置值)产生了几种形貌的等离子体羽(弥散圆锥状、丝加晕形、念珠串状和空心锥状),从而进一步丰富了等离子体羽的形貌.通过对比放电的电压和发光信号波形,发现除丝加晕形等离子体羽外,其他3种等离子体羽在每个外加电压周期均放电1次.不同的是,弥散圆锥状和念珠串状等离子体羽的放电出现在电压负半周期,为负放电.而空心锥状等离子体羽的放电出现在外加电压正半周期,为正放电.丝加晕形等离子体羽每个电压周期存在1个负放电和1个正放电.此外,还利用高速成像设备对这几种形貌等离子体羽的时空演化进行了研究.相关结果表明,负放电对应负流光的传播过程,而正放电对应正流光的过程.视觉上不同形貌的等离子体羽是正流光、负流光及其组合时间叠加的结果.本文的结果对大气压等离子体射流中等离子体羽形貌的深入研究及流光动力学的进一步发展均具有重要价值.
Atmospheric pressure plasma jet has the ability to generate a kind of remote plasma in open air, also referred to as plasma plume, which is abundant with active species. The plasma jet has extensive application prospects in various fields, such as material synthesis, surface modification, biomedicine, and environmental protection, etc. The morphology of plasma plume is related with the distribution of active species, which is important for the investigation of plasma jet.Up to now, only a few plume morphologies have been observed in experiment. Aim to this status, an argon plasma jet is utilized to investigate the plume morphology in this paper. With varying voltage parameters including amplitude, frequency and biased value, several morphologies are observed for the first time, such as a diffuse cone, a corona and a central filament(DAF), a bead string, and a hollow structure. These results obviously enrich the plume morphology. Through comparing their waveforms for the different morphologies, it is found that plasma plume with the other three morphologies(except the DAF)presents one emission pulse per voltage cycle. Moreover, the emission pulse appears at the negative half cycle,corresponding to a negative discharge for the diffuse cone and the bead string. However, the hollow plume presents the emission pulse at the positive half cycle(a positive discharge). As a comparison, there are two emission pulses for the DAF plume, one of which is a negative discharge and the other corresponds to a positive discharge. In addition, spatial and temporal evolutions are conducted by an emICCD for the different plumes. Results reveal that the negative discharge corresponds to a negative streamer, while the positive discharge is a positive streamer. The different morphologies observed by naked eyes are temporally integrated results of the negative streamer and the positive streamer. These results are of great significance for the profound investigation of plume morphology and further study of streamer dynamics.
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