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

Abstract

The optical emission spectroscopy study of a pulsed atmospheric pressure discharge source in argon and an argon–hydrogen mixture is performed. The discharge source has needle-to-cylinder configuration with cathodes made of brass and stainless steel. Numerous metallic lines are identified in the discharge spectra (Cu, Zn, Fe, Cr, V, and W) in the 260–800 nm spectral range. A thorough study of electron temperature T_e by means of Fe I line intensity distribution is performed. The results showed that T_e = 7000 K–9000 K, which was also confirmed using Fe II and Cu I lines. The agreement with the T_e results obtained using the ionic-to-atomic line ratio method is achieved. Several broad spectral lines originating from the cathode material (Cu I, Cu II, and Fe I) are revealed in the discharge spectra and described using an appropriate fitting function. For those with reliable spectral line broadening data (e.g. Cu I 448.0 nm and Fe I 538.3 nm lines), the electron number density N_e diagnostics procedure is applied. By means of a spectral line deconvolution procedure, the values N_e = (0.9–1.5) × 10¹⁶ cm⁻³ and N_e = (7–10) × 10¹⁶ cm⁻³ are measured from the cathode regions of the discharge. The agreement between the N_e results obtained from Stark halfwidth and Stark shift results is achieved. The addition of hydrogen (3% by vol.) changed the yield of metallic lines which is more emphasized in the case of the stainless steel cathode.