Flux dependence of deuterium retention in single crystal tungsten

The retention of deuterium in single crystal tungsten has been measured as a function of the incident ion flux in the range of 1×1017–5×1019 D+/m2 s at 300 K. Incident D3+ ions were implanted to fluences of 1021, 1022, and 1023 D+/m2 with ion energies (500 eV/D+) below the threshold energy for elastic collision damage. Above 3×1018 D+/m2 s, little or no flux dependence is seen. However, a rapid decrease in retention is seen for incident fluxes below 1018 D+/m2 s at the 1021 D+/m2 fluence, suggesting a threshold value below which retention is strongly reduced. Flux dependence at the higher fluences show a smaller decrease in retention with decreasing flux. The observed results are consistent with trapping and trap evolution by cluster and cavity formation. The effect of specimen surface preparation has proved to be very significant, especially for the lower fluence.