Hydrogen isotope ratios measurements by Penning gauge spectroscopy of molecular Fulcher-α band

Abstract

Penning gauge spectroscopy of Balmer-α lines of hydrogen isotopes is widely used in fusion experiments to determine the hydrogen isotope ratios and the partial pressures in the pump duct. The Balmer-α line isotopic shifts are very small < 0.176 nm and the lines partially overlap because of the presence of energetic atoms produced by molecular dissociation. The ro-vibrational emission bands of each hydrogen isotopomer consist of many narrow spectral lines, covering a wide wavelength span and have an unique signature. To investigate the capability of the hydrogen molecular spectroscopy for the isotopic ratio determination, an Alcatel-type Penning gauge was coupled by the optical fiber to the Echelle spectrometer having 365–715 nm spectral range and the spectral resolving power above 20,000. The intensities of both atomic Balmer-α lines and molecular Fulcher-α bands were measured in the range of 6·10−6 – 4·10-3 mbar. The rotational and vibrational populations were almost independent of the gas pressure below 2·10-4 mbar. The total intensities of the Fulcher-α molecular bands were linearly proportional to the gas pressure. The H2 and D2 molecular emission in 599–639 nm spectral range were in a good agreement with the isotopic composition of the used gas mixtures.