Permeation rates of H/He through a Pd foil for isotope separation applications in the exhaust stream of a fusion reactor

The Princeton Field-Reversed Configuration fusion experiment is a type of magnetic confinement device that utilizes odd-parity rotating magnetic fields to induce closed field lines. The D-³He fuel is aneutronic, however, deuterium (D) atoms in the plasma can fuse with each other to produce either tritium (T) or ³He. The T must be extracted in order to have a low radioactivity plasma, and in the future, it can then be stored, and breed more ³He fuel through its decay. One way of separating hydrogen (H) and helium (He) isotopes is by introducing a high Z material – permeation barrier – high Z material configuration, where the permeation barrier, such as Al₂O₃, will prevent high energy ions from diffusing back into the plasma. High Z, large surface area materials, such as Palladium (Pd), have high permeability of H and He and low sputtering yields. Pd has a high H sorption rate and high permeability through conversion to a metallic hydride when heated to high temperatures, which increases H diffusion. Under these conditions, surface oxides and carbides of Pd may dissolve, decreasing surface impurities. We will report data on H/He permeability in Pd foil at a temperature range of 300-800 K, focusing on the effects of pressure and temperature.