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

Penning gauge spectroscopy of Balmer-alpha 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-alpha 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-alpha lines and molecular Fulcher-alpha 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-alpha molecular bands were linearly proportional to the gas pressure. The H-2 and D-2 molecular emission in 599-639 nm spectral range were in a good agreement with the isotopic composition of the used gas mixtures.