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AbstractDeuterium permeation studies for polycrystalline tungsten foil have been conducted to provide data for estimating tritium transport and trapping in tungsten-clad divertors proposed for advanced fusion-reactor concepts. Based on a detailed transmission electron microscopy (TEM) microstructural characterization of the specimen material and on analyses of permeation data measured at temperatures ranging from 610 to 823 K for unannealed and annealed tungsten foil (25 µm thick), we note the following key results: (1) deuterium transport in tungsten foil is dominated by extensive trapping that varies inversely with prior anneal temperatures of the foil material, (2) the reduction in the trapped fraction correlates with a corresponding elimination of a high density of dislocations in cell-wall structures introduced during the foil fabrication process, (3) trapping behavior in these foils can be modelled using trap energies between 1.3 eV and 1.5 eV and trap densities ranging from 1 × 10−5 to 7 × 10−5 atom fraction. Notesa Work supported by U. S. Department of Energy, Director of Energy Research, Office of Fusion Energy under Contract DE-AC07-76ID01570.