Morphology transition from diffuse to diffuse-and-filamentary for an argon plume with varying sinusoidal frequency or voltage amplitude

Abstract

With increasing sinusoidal frequency or its voltage amplitude, a central filament emerges in a diffuse plume downstream of an argon jet with a single-electrode geometry. The plume with a co-existing filament and diffuse part, also referred to as a diffuse-and-filamentary (DAF) plume, is formed after a sudden length increment from a diffuse plume. Only one negative discharge appears per voltage cycle for the diffuse plume. Besides the negative discharge, there is one positive discharge per voltage cycle for the DAF plume. By fast photography, negative discharge behaves as plump plasma bullets propagating along the argon flow, which results in diffuse plume or the diffuse part of the DAF plume. Comparatively, positive discharge behaves as slim bullets, leading to the filament formation. Based on optical emission spectroscopy, it is found that both electron density and electron temperature increase with increasing sinusoidal frequency or voltage amplitude for negative and positive discharges. Moreover, there are abrupt increments in them for negative discharge during the morphology transition. Compared with negative discharge, the positive one has higher electron density and electron temperature. All of the experimental phenomena mentioned above are qualitatively explained through considering the discharge enhancement by residual active species.

Influence of oxygen addition on the discharge characteristics of an argon plasma jet at atmospheric pressure

“…As is well known, both negative and positive discharges of plasma jet operate in a streamer regime. [1,20,24,[27][28][29][30]54] Compared with negative discharge (anode-directed streamer), positive discharge (cathode-directed streamer) has a higher electric field strength (E). [29,55] Electrons are mainly produced in the plasma through the impact of argon atoms by electrons, which is dominated by the first Townsend ionization coefficient (α).…”

“…[19] The formation of plasma bullet is attributed to a streamer regime. [20] In addition to discharge regime, various discharge characteristics, such as plume length, [21][22][23][24] plume morphology, [25][26][27][28][29][30] and plasma parameters, [27][28][29][31][32][33] are investigated for inertgas plasma jet.…”

Discharge aspects of a snake‐like plasma plume generated by an atmospheric pressure plasma jet with variable argon flow rate

“…[7] Due to its flexibility and low cost, plasma jet has become a promising tool for the applications in biomedicine, [8,9] material synthesis, [10][11][12] surface modification, [13][14][15] light source, [16] and water purification. [17][18][19] Plasma jet is normally fed with inert gas, such as helium, [20][21][22] argon, [23][24][25][26] neon, [27][28][29] and so on. When helium is used, the plasma plume is diffuse, [30] which means that no filament can be found in the plume.…”

“…However, the plasma plume is constricted to a filament when argon is used. [31,32] Although the above-mentioned plumes, diffuse or filament, are continuously luminous to naked eyes, [26,33] fast photography reveals that they consist of discrete fast-moving plasma bullets. [34,35] To explain the formation of the plasma bullets, a streamer regime is proposed.…”

“…Plasma jet is normally fed with inert gas, such as helium, [ 20–22 ] argon, [ 23–26 ] neon, [ 27–29 ] and so on. When helium is used, the plasma plume is diffuse, [ 30 ] which means that no filament can be found in the plume.…”