Atmospheric microwave-induced plasmas in Ar/H₂ mixtures studied with a combination of passive and active spectroscopic methods

Abstract

Several active and passive diagnostic methods have been used to study atmospheric microwave induced plasmas created by a surfatron operating at a frequency of 2.45 GHz and with power values between 57 and 88 W. By comparing the results with each other, insight is obtained into essential plasma quantities, their radial distributions and the reliability of the diagnostic methods. Two laser techniques have been used, namely Thomson scattering (TS) for the determination of the electron density, n e , and temperature, T e , and Rayleigh scattering (RyS) for the determination of the heavy particle temperature, T g . In combination, three passive spectroscopic techniques are applied, the line broadening of the H β line to determine n e , and two methods of absolute intensity measurements to obtain n e and T e . The active techniques provide spatial resolution in small plasmas with sizes in the order of 0.5 mm. The results of n e measured with three different methods show good agreement, independent of the plasma settings. The T e values obtained with two techniques are in good agreement for the condition of a pure argon plasma, but they show deviations when H 2 is introduced. The introduction of a small amount (0.3 %) of H 2 into an argon plasma induces contraction, reduces n e , increases T e , enhances the departure from equilibrium and leads to conditions that are close to those found in cool atmospheric plasmas.

Experimental investigation of the electron energy distribution function (EEDF) by Thomson scattering and optical emission spectroscopy

“…The axial trend in T e (TS) found along the SW discharge is part of a larger category that can be denoted by the trend of rising T e (TS) in outer plasmas parts. This was also observed experimentally in studies on atmospheric pressure plasmas (see for instance [17,62,68,70,71]) but also for low-pressure plasmas [38,42]. In outer regions where n e drops, the (mean) T e values go up.…”

“…This coefficient is determined from the CRM where all important production and loss mechanisms of some given states are included. We use here an updated cross sections database for the CRM [60] compared with the previous studies [33,58,61,62]. The electron temperature obtained via this method is the effective Maxwellian temperature needed to sustain the excitation-ionization efflux through the argon excitation space.…”

Laser scattering on an atmospheric pressure plasma jet: disentangling Rayleigh, Raman and Thomson scattering

“…The different species in the plasma, such as electrons and heavy particles, are probed directly by the laser, providing a reliable method for measuring densities and temperatures. This was shown recently for these non-thermal plasmas by Palomares et al [5].…”

Spatially-Resolved Spectroscopic Diagnostics of a Miniature RF Atmospheric Pressure Plasma Jet in Argon Open to Ambient Air

“…Electron temperature is an essential parameter to characterize when studying APPJs, but is nonetheless not always straightforward to estimate. The most common experimental techniques reported are the line-ratio method assuming Boltzmann equilibrium [45][46][47], the Boltzmann-plot method [46,47], the equivalent circuit model coupled with the power balance equation [48], and CR models similar to the one used in the present study [33,49,50]. As can be seen in the next lines, these multiple techniques can provide a wide range of T e values, but depending on the conditions, not all are always reliable.…”