Deuterium trapping by defects in W polycrystalline foils during ion bombardment was investigated by thermal desorption spectroscopy using the low fluence probe method. Probe TDS spectra showed, that there are at least 6 peaks in the region 350-900 K: at 370 K, 450 K, 530 K, 580 K, 630 K, 750 K. Experiments with as received samples showed that D is trapped mainly in low energy traps in the region 390-650 K. These defects are attributed to technological defects such as dislocations and vacancies. The peak at 750 K easily disappears when annealing the sample at about 1300 K and can be attributed to vacancy clusters. The peak at 630 K irreversibly increases at high fluence, it also appears when annealing the sample above 1300K. This peak can be attributed to voids. Voids of about 20 nm in diameter in the near surface region were observed by FIB/SEM in cases when 630 K peak was observed.

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