Hydrogen isotope exchange mechanism in tungsten studied by ERDA

Future fusion reactors use a D-T plasma mixture as fuel. A fraction of hydrogen species can escape the plasma confinement and hit the first wall. Hydrogen isotope exchange, a process in which trapped T atoms are replaced with lighter hydrogen isotopes D or H, is a potential method to minimize radioactive T retention in the wall materials. The present work extends our systematic research on isotope exchange by reversing the process, i.e. by implanting H ions into tungsten followed by subsequent annealing at different constant temperatures in D-2 atmosphere. Elastic Recoil Detection Analysis was used to determine the H and D concentrations. The results show that the isotope exchange process takes place regardless of the mass of the active hydrogen isotope. This indicates that the isotope exchange is a statistical phenomenon in which the abundance of the neighboring hydrogen near the trapped hydrogen isotope defines the efficiency of the process.