2020 CAP Virtual Sessions / Sessions virtuelle de l'ACP 2020

Non-equilibrium nature of argon-based radiofrequency and microwave plasmas at atmospheric pressure evidenced by hyperfine optical emission spectroscopy

9 Jun 2020, 12:55

20m

Virtual Platforms

Oral Competition (Graduate Student) / Compétition orale (Étudiant(e) du 2e ou 3e cycle) Symposia Day (DPP) - Plasma Physics DPP-1 : Plasma Physics Symposium

Speaker

Mr Francis Labelle (Université de Montréal)

Description

In this work, the non-equilibrium nature of argon-based radiofrequency (RF) and microwave plasmas at atmospheric pressure is evidenced. In particular, rotational temperature ($T_{rot}$) and neural gas temperature ($T_g$) are found to be unequal in every condition tested, even though they are often assumed equal in such plasmas in the literature. Such a finding was made possible through the use of a hyperfine spectrometer developed and commercialized by LightMachinery Inc. Offering a 2 pm resolution over a simultaneous range of 25 nm, it was tuned to the 820-845 nm range in which the broadening of the Ar $2p_2-1s_2$ and Ar $2p_3-1s_2$ (Pashen notation) transitions is strongly affected by the neutral gas temperature. Therefore, for these emission lines, the experimental broadening was much smaller than the other broadening sources, ensuring a precise and accurate determination of $T_g$.

The microwave plasmas were produced inside a fused silica tube using a surfaguide-type wave launcher, while the RF plasmas were produced inside a fused silica tube placed between two electrodes. In both cases, an admixture of $H_{2}O$ or $N_2$ were added to the argon flow in order to observe either the OH ($A^2{\Sigma }^{+}-X^2{\Pi }_i$) or the $N_2^{+}$ ($B_2{\Sigma }_u^{+}-X_2{\Sigma }_g^{+}$) molecular systems. A rotational temperature was then calculated using the Boltzmann plot method. $T_{rot}$ and $T_g$ values were obtained every centimeter along the plasma columns. For the microwave plasma with an admixture of $H_{2}O$, $T_g$ values of over 2000 K were obtained while $T_{rot}$ values were in the 1400 K range. For the microwave plasma with an admixture of $N_2$, $T_{rot}$ values were found to rise to ~3200 K whereas $T_g$ values only increased to ~2400 K. The same discrepancies were found in the much colder RF plasmas ($T_g$~400 K while $T_{rot}$~515 K). Therefore, since the rotational temperatures did not equal the gas temperature in every condition tested, it is concluded that the rotational-translational equilibrium cannot not be assumed for RF and microwave argon-based plasmas at atmospheric pressure.

Presentation materials

ConferenceCAPFrancisLabelle.pdf