  Retention of hydrogen isotopes (protium, deuterium and tritium) in tungsten
is one of the most severe issues in design of fusion power plants, since
significant trapping of tritium may cause exceeding radioactivity safety limits
in future reactors. Hydrogen isotopes in tungsten can be detected using the
nuclear reaction analysis method in channeling mode (NRA/C). However, the
information hidden within the experimental spectra is subject to
interpretation. In this work, we propose the methodology to interpret the
response of the experimental NRA/C spectra to the specific lattice locations of
deuterium by simulations of the NRA/C spectra from atomic structures of
deuterium lattice locations as obtained from the first principles calculations.
We show that trapping conditions, i.e., states of local crystal structures
retaining deuterium, affect the lattice locations of deuterium and the change
of lattice locations can be detected by ion channeling method. By analyzing the
experimental data, we are able to determine specific information on the
deuterium trapping conditions, including the number of deuterium atoms trapped
by one vacancy as well as the presence of impurity atoms along with deuterium
in vacancies.
