Hydrogen Isotopic Ratio by Residual Gas Analysis During the JET DT Campaigns

The analysis of the hydrogen isotopes content provides essential information about the fusion device operation. In the core plasma side, hydrogen isotopic analysis is provided by spectroscopic and by neutron-techniques diagnostics. For the exhaust gas it is carried out by mass spectrometry from residual gas analyzers (RGA) and by optical gas analysis (OGA) using a Penning gauge. The use of traditional quadrupoles mass spectrometers for RGA poses serious problem in discharges with tritium gas because of the overlap of the signal of different hydrogen molecules at the same mass number. The paper describes a novel technique to disentangle this difficulty by a cross-related analysis of RGA data with the OGA results. Another affecting concern in mass spectrometry analysis are due to the instrument different sensitivity respect to the gas mass number. The paper provides the results the gas calibration data for all the quadrupoles employed in the JET gas analysis. The hydrogen isotopic ratio are calculated from RGAs detected currents by means of simple formulas. The results of this procedure have been provided for selected DT JET discharges versus the JET time base and compared with the same optical data. Time averaged hydrogen isotopic ratio values have been calculated for a large number of discharges during the DT and T campaigns.