中频正弦电压下大气压氦等离子体射流的产生机理

Formation Mechanism of Helium Plasma Jet at Atmospheric Pressure Under Medium-frequency Sinusoidal Voltage

为了探讨He大气压等离子体射流(APPJ)的产生机理,采用增强型电荷耦合元件(ICCD)分别拍摄HeAPPJ的纵截面和横截面图像发现,He在17kHz中频正弦外施电压下正负半周的APPJ图像不对称,在正半周电压下,He APPJ以空间流光的形式向石英管口传输,至石英管外转换为沿He/Air界面传输的沿面放电;而在负半周电压下,He APPJ传播较正半周下短,为一种典型的存在于He气流中的电晕放电现象。研究APPJ长度与管内介质阻挡放电(DBD)放电模式的关系发现,随着外施电压的升高,DBD放电将依次呈现出"倍周期"、"混沌"、"流光-辉光过渡"、"非对称辉光"、"对称辉光"和"辉光+丝状"等6种模式,各个模式的放电电流波形具有不同的特征,等离子体羽流长度并不是单纯地随着外施电压增大而增长的量,而是放电所产生的He激发态粒子浓度与放电对气流的扰动两方面共同作用的结果。

In order to discuss the formation mechanism of He atmospheric pressure plasma jet （APPJ）, the intensified CCD （ICCD） is employed to shot the longitudinal and axial section of He APPJ. It is found that, the He APPJ is not symmetrical under positive and negative cycles of applied voltage of 17kHz Sin wave. Under positive cycle, the He APPJ which is formed as space streamer at the edge of an active electrode propagates to the nozzle of quartz tube, and then it transits to the surface discharge of which the propagation appears along the interface between He and Air in the ambient. However, under negative cycle of applied voltage, the propagation length of the He APPJ is much shorter than that under positive cycle, which presents as a classic corona discharge in He flow. Furthermore, the relationship of APPJ length and discharge modes of dielectric barrier discharge （DBD） inside tube is also investigated. With the increment of applied voltage, 6 kinds of discharge modes such as the ＇6period- doubling＂, ＂chaotic＂, 6＇streamer transit to glow＂, ＂unsymmetrical glow＂, ＂symmetrical glow＂, and ~＇glow and filament＂, appear successively, possessing different characteristics and properties in discharge current waveforms. The length of plasma plume is not only caused by the applied voltage alone but actually determined by the excited He particles density during the discharge and disturbance of gas flow caused by discharge.