A simple spectroscopic method to determine the degree of dissociation in hydrogen plasmas with wide-range...

A new and simple method for determining the degree of dissociation in hydrogen plasmas is presented. In this method, wide-range spectrum covering from an atomic H-γ line (434.05 nm) to molecular Fulcher-α band (600-640 nm) is measured simultaneously by a wide-range miniature spectrometer. Since the wide-range spectrum measured by the miniature spectrometer is too broadened to resolve respective lines in the Fulcher-α band, a synthetic spectrum method is applied to improve the accuracy in the Q-branch of Fulcher-α band intensity measurement. In order to reduce the influence from other transitions or anomalous P- and R-branch of Fulcher-α spectrum, the Fulcher-α spectra of which vibrational states are higher than 1 (υ ≥ 1) are synthesized using the rotational temperature obtained by the 0-0 Fulcher-α spectrum. The degree of dissociation is determined from the intensity ratio between H-γ line and the synthesized Fulcher-α band spectrum. A comparative study carried out in a volume-produced negative hydrogen ion source shows that the degree of dissociation determined by this method agrees well with the measured values using a spectrometer with high spectral resolution. The present method is expected to be useful to characterize the plasma sources with molecular species since it provides important parameters for understanding neutral particle behaviors.