A uniform laminar air plasma plume with large volume excited by an alternating current voltage

Abstract

Using a plasma jet composed of two needle electrodes, a laminar plasma plume with large volume is generated in air through an alternating current voltage excitation. Based on highspeed photography, a train of filaments is observed to propagate periodically away from their birth place along the gas flow. The laminar plume is in fact a temporal superposition of the arched filament train. The filament consists of a negative glow near the real time cathode, a positive column near the real time anode, and a Faraday dark space between them. It has been found that the propagation velocity of the filament increases with increasing the gas flow rate. Furthermore, the filament lifetime tends to follow a normal distribution (Gaussian distribution). The most probable lifetime decreases with increasing the gas flow rate or decreasing the averaged peak voltage. Results also indicate that the real time peak current decreases and the real time peak voltage increases with the propagation of the filament along the gas flow. The voltage-current curve indicates that, in every discharge cycle, the filament evolves from a Townsend discharge to a glow one and then the discharge quenches. Characteristic regions including a negative glow, a Faraday dark space, and a positive column can be discerned from the discharge filament. Furthermore, the plasma parameters such as the electron density, the vibrational temperature and the gas temperature are investigated based on the optical spectrum emitted from the laminar plume.

A double‐mode planar argon plume produced by varying the distance from an atmospheric pressure plasma jet

“…As time lapses, two new filaments will be born and repeat the same process mentioned above. As pointed out in the literature [27, 34], the filamentary‐mode plume is gas flow driven, whose moving velocity roughly equals to that of the rectangular stream.…”

“…For example, gas temperature (T g ) and vibrational temperature (T vib ) are diagnosed using optical emission spectra for planar plumes in the streamer mode [30][31][32]. For the filamentary-mode planar plume, electron density (n e ) has been estimated to be in an order of 10 14 cm −3 [33][34][35]. Through a fibre thermocouple, gas temperature of the plume is estimated to be several hundred K [25,36].…”

Generation of a planar direct-current glow discharge in atmospheric pressure air using rod array electrode

“…Instrumental broadening at 491 nm line is measured by a mercury lamp with a slit width of 100 μm 28 . Figure 6(a) indicates a de-convolution procedure to obtain the Stark broadening of H β 33 . Its full width at half maximum (Δ λ S ) is 0.0310 nm for the positive column of discrete discharges with 2.5 mm W g .…”

Influence of humidity on the characteristics of laser-induced air plasma

“…15) The van der Waals broadening can be negligible because of the high plasma temperature. 51) The Doppler broadening follows a Gaussian profile and depends on the plasma temperature in K, which can be expressed as 32) Á Doppler…”