Effect of post-D+-irradiation time delay and pre-TDS heating on D retention in single crystal tungsten

Deuterium retention measurements using thermal desorption spectroscopy were made for single crystal tungsten (SCW) irradiated with D+ to a fluence of 1 × 1023 D/m2 at room temperature following various experimental procedures. The dominant desorption peaks in the TDS spectra were at ∼400 K and ∼600 K, with a peak at ∼500 K also present in some cases. The primary findings were (i) D retention was found to decrease by as much as a factor of 2 with increasing the time delay between D+ irradiation and TDS from <1 h to >8 weeks, indicating the presence of some mobile D in the bulk introduced during irradiation, which could diffuse and escape even at room temperature. (ii) Mild baking of the test chamber to ∼360 K between D+ irradiation and TDS resulted in the escape of ∼40% of the trapped deuterium, indicating that additional lower energy traps exist. (iii) Background gas impurities lead to impurity implantation in the near surface of the specimen, which in turn leads to increased trapping of D. However, the effect of impurities on D retention was relatively smaller (about 10–20%) than the effects of mild baking and post-implantation time delay.