Effect of the gas flow rate on the spatiotemporal distribution of Ar(1s₅) absolute densities in a ns pulsed plasma jet impinging on a glass surface

Abstract

This work presents spatial (axial-z and transversal-y) and temporal distributions of Ar(1s 5 ) metastable absolute densities in an atmospheric pressure argon micro-plasma jet impinging on an ungrounded glass surface. Guided streamers are generated with a DBD device driven by pulsed positive high voltages of 6 kV in amplitude, 224 3  ns in FWHM and 20 kHz in frequency. The argon flow rate is varied between 200 and 600 sccm. The glass plate is placed at 5 mm away from the reactor's nozzle and perpendicular to the streamers propagation. At these conditions, a diffuse stable discharge is established after the passage of the streamers allowing the quantification of the Ar(1s 5 ) absolute density by means of a conventional TDLAS technique coupled with emission spectroscopy and ICCD imaging. The good reproducibility of the absorption signals is demonstrated. The experiments show the strong dependence of the maximum density 0.5 4 10 cm 13 3-´-() on the gas flow rate and the axial and transversal position. At 200 sccm, high maximum densities 2.4 10 cm 13 3 >´-() are obtained in a small area close to the plasma source, while with increasing flow rate this area expands towards the glass plate. In the transversal direction, density maxima are obtained in a small zone around the propagation axis of the streamers. Finally, a noticeable increase is measured on the Ar(1s 5 ) effective lifetime close to the glass surface by varying the flow rate from 200 to 600 sccm. In overall, the effective lifetime varies between ∼25 and ∼550 ns, depending on the gas flow rate and the values of z and y coordinates. The results obtained suggest that the present system can be implemented in various applications and particularly in what concerns the detection of weakly volatile organic compounds present in trace amounts on different surfaces.

Ar(1s5) absolute radial densities in a ns‐pulsed argon plasma jet impinging on dielectric targets at floating potential – plasma action on organic molecules

“…Figure illustrates the experimental setup used in this work. The APPJ was produced using a coaxial Dielectric Barrier Discharge (DBD) reactor, which has been described in more detail elsewhere . Briefly, it contained a quartz dielectric tube and a stainless‐steel hollow cylinder (biased electrode), which was placed tightly inside the quartz tube.…”

“…But, again, this was done in the absence of a target and without giving any information about the radial distribution of the Ar(1s 5 ) absolute density. It should be noted that our group has studied recently a ns‐pulsed Ar APPJ impinging on a floating‐potential glass plate . It was demonstrated that the residual plasma column left by the streamers is well diffuse and reproducible.…”

“…APPJs can be obtained through the excitation/ionization of a noble gas (usually argon or helium) by means of rf, kHz‐sinusoidal and ‐pulsed high voltages (HV) . Besides, they exhibit interesting properties for applications in biomedicine, agriculture, and interactions with inert targets . In the latter applications, the plasma impinges on different liquid and solid surfaces.…”

“…The role of metastable atoms in APPJs is particularly significant . They have relatively high energies, and act as energy reservoirs, contributing significantly to the plasma chemistry.…”

“…However, Ar APPJs are often filamentary, and the accurate mapping of Ar m absolute densities is therefore challenging. Different works have shown that this can be achieved using TDLAS in specific APPJ configurations . However, the vast majority of published studies refer to APPJs driven mostly by rf or kHz‐sinusoidal voltages without studying the effect of different targets.…”