Q-branch of fulcher-α diagonal bands for determination of the axial temperature distribution in the cathode sheath region of hydrogen and hydrogen-argon abnormal glow discharge

Abstract

In this paper, we present results of rotational, vibrational, and gas temperature distribution study in the cathode-sheath region of an abnormal glow discharge in hydrogen and hydrogen-argon mixture. For this purpose, we used Q-branch of the Fulcher-α diagonal bands d3Π−u, ν′=0, 1, 2, 3→ a3Σ+g, ν″=0, 1, 2, 3. The boundary between the cathode sheat and negative glow region is determined as the position where the electric field strength falls to zero. For the electric field measurement Stark polarization spectroscopy of hydrogen Balmer alpha line was employed and the thickness of cathode sheat is estimated by fitting the experimentally obtained distribution of electric field strength to a suitable model function.The temperature values, measured in the cathode sheath from different vibrational bands, decrease with vibrational quantum number v′ increase. The vibrational temperature is determined from the relative intensities of vibrational bands of the Fulcher-α system (d3Π−u→ a3Σ+g electronic transition; Q-branch v′= v″=2 and v′= v″=3). Temperature distributions along the axis of the cathode sheath are also reported and discussed. The distributions of rotational temperature show that all three temperatures (gas, rotational and vibrational) vary along the cathode sheath region of discharge and that all four bands give consistent values for the rotational temperature. The measurements performed with high spectral resolution provide further insight into understanding or modelling the DC glow discharge. The reported results represent the contribution to the development of the spectroscopic method for gas temperature measurement.