The investigation of fast hydrogen atoms created in low pressure pulsed discharge in hydrogen-containing gas mixtures by means of Hα line Doppler spectroscopy

Abstract

Doppler spectroscopy of the H_α line is used for the study of fast hydrogen atoms created in a novel gas discharge source operating at lower pressure in hydrogen-containing gas mixtures. The discharge is formed around the rod shaped cathode in pulsed high voltage regime with the possibility to change pulse width, duty cycle and electric parameters. The cathodes made of copper, stainless steel, aluminum and graphite are used in the frame of this study. In case of argon carrier gas, the fitting function consisting of two Gaussian profiles is applied and the side-on H_α profiles (observation angle 90° relative to the surface normal) are analyzed in order to measure mean kinetic energy, maximum gained energy and the contribution of fast excited atoms to overall H I profile. The pedestal of the H I line reflects the presence of fast H* atoms in the discharge. From the end-on H I profiles (observation along the surface normal), the maximum H* energy is deduced and compared with the side-on results. The radial distribution of fast H* depicted the linear decrease of mean kinetic energy near the cathode surface as well as the strong dependence of excessive broad component area with gas pressure. In case of H₂, H₂ + 5 % Ar and Ne+0.8 % H₂, the overall fit comprises three Gaussian components. In case of graphite cathode, the mean kinetic energies are 37 eV (Ar + 3 % H₂), 102 eV (H₂ + 5 % Ar), 76 eV (N₂ + 5 % H₂), 167 (Ne+0.8 % H₂) and 180 eV (H₂). The energy of fast H* atoms with the graphite cathode (the maximum voltage not exceeding 750 V) has the lowest value mainly due to low values of energy reflection coefficients. The maximum energy gained in the sheath (∼425 eV) is achieved for the copper cathode and neon‑hydrogen mixture.