Hydrogen isotope analysis by quadrupole mass spectrometry

Abstract

The analysis of isotopes of hydrogen (H,D,T) and helium (3He,4He) and selected impurities using a quadrupole mass spectrometer (QMS) has been investigated as a method of measuring the purity of tritium gas for injection into the Tokamak Fusion Test Reactor (TFTR). A QMS was used at low resolution, m/Δm<150, for quantifying impurities from m/q = 2 to 44, and at medium resolution, m/Δm∠600, for determining concentrations of HD in 3He, and 4He in HT/D2. Sample gases to be studied were introduced into the QMS housing through a molecular leak from a 3‐liter inlet volume. A linear relation between peak height (and area) and component partial pressure was verified and QMS sensitivities for various ions were determined. Increases in background hydrocarbon and water vapor were measured whenever hydrogen (any isotope) was present in the QMS housing. Baking and H2 glow discharge conditioning (GDC) minimized these effects. Low resolution, computer‐controlled QMS analysis of D2 and T2 standard mixtures after H2/GDC treatment demonstrated the capability to verify tritium purity at the 98 at.% level as required in the TFTR application. Detection limits quoted were 0.005 mol.% for Ar; 0.02 mol.% for CT4, 02 and CO2; 0.05 mol.% N2/CO; and between 0.03 and 0.25 mol.%, depending on the sample, for hydrogen and helium species.