Effect of atmospheric pressure pulsed discharge spatial inhomogeneity on Ar I and H I lines: Electron number density study

Abstract

The spatial inhomogeneity of pulsed atmospheric pressure discharge in argon is investigated using the electron number density Ne diagnostics procedure applied to asymmetrically broadened Ar I lines. A dedicated fitting procedure is used for describing Ar I 703.0 nm line shape recorded from argon gas discharge and H I (at 486.13 and 656.28 nm) lines recorded from Ar‐H2 gas mixture discharge. The results revealed the change in Ne in both axial and radial directions. The additional Ar I lines at 614.5, 710.7, 731.2, and 731.6 nm, recorded from integral spatial radiation, are analysed as well to confirm the results from the plasma column region. The possibility of using AlO (B2∑+–X2∑+) and CN (B2∑+–X2∑+) molecular bands for gas temperature Tg measurements in this type of gas discharge source is demonstrated and Tg used as an input parameter for the Ne diagnostics procedure. For the proper identification of molecular band spectral lines, the Fortrat parabolas are constructed. The results obtained from Ar I 703.0 nm line indicate three different Ne values, with Ne1 ≈ 0.6 × 1016 cm−3, Ne2 ≈ 3.6 × 1016 cm−3, and Ne3 ≈ 19 × 1016 cm−3 measured from the plasma column. These Ne values increase in the cathode and anode region.

The spectroscopic study of metallic lines emitted from a pulsed atmospheric pressure gas discharge source with brass and stainless steel cathodes

“…However, from Fig. 10 in Jovović et al , 13 one may notice that similar low N e is obtained by applying the same fitting procedure on the narrow H I line component (recorded from argon NTC). This is the electron density of a peripheral zone of the discharge.…”

“…The lowest N e measured from the narrowest Cu I Voigt prole seems to correspond to the discharge zone not detectable in the case of the SS cathode. However, from Fig.10in Jovović et al,13 one may notice that similar low N e is obtained by applying the same tting procedure on the narrow H I line component (recorded from argon NTC). This is the electron density of a peripheral zone of the discharge.…”

“…The fitting function represents the superposition of 3 mutually shifted Voigt profiles; the same procedure was applied to Ar I lines in previous work. 13 For these two lines, the Gaussian halfwidth ( W G ) is 0.016 nm and Lorentzian FWHM i.e. W P = 0.0072 (0.0077) nm.…”

“…The peculiarity of the pulsed NTC discharge source is the radial and axial inhomogeneity, as shown for Ar I lines emitted from the cathode, anode and plasma regions. 13 In the case of the cathode region, for those lines with significant Stark broadening parameters, one may expect larger FWHM and a complex spectral line shape in comparison to surrounding lines. In Fig.…”

“…12 Recently, a novel needle-to-cylinder (NTC) discharge source at atmospheric pressure driven by a ms-pulsed generator unit was developed. 13 The NTC discharge structure comprises a nearcathode region, negative glow (plasma column) and an anode region. The study of broad Ar I lines has shown that N e spatial inhomogeneity exists in the discharge whilst the gas temperature remains constant (1500-1750 K).…”