Hydrogen and helium trapping in tungsten under single and sequential irradiations

The trapping of hydrogen and helium in polycrystalline tungsten irradiated with 500 eV He+, H+ and D+ ions, individually or sequentially, has been measured by thermal desorption spectroscopy. Specimens irradiated with 500 eV He+ at 300 K show three He release peaks in the vicinity of similar to 500, similar to 1000, and similar to 1200 K. The helium is thought to form He vacancy complexes or bubbles. Increasing the specimen temperature to 700 K does not significantly affect the trapping behavior of He. Sequential He+-D+ irradiation at 300 K results in the elimination of He release above 800 K. Instead, both D and He were released in the range 400-800 K. This is interpreted as interstitial D and He released from the near surface. Sequential He+-D+ irradiation at 700 K resulted in a reduced single He peak at similar to 1000 K with very little release observed below 800 K; no D was trapped for irradiations at 700 K. Sequential D+-He+ irradiations at 300 K show that He trapping occurs in much the same manner as for the He+-only case while D retention is reduced at the near surface. Sequential D+-He+ irradiations at 700 K indicate that pre-irradiation with D+ has little or no effect on the subsequent trapping behavior of He. (c) 2006 Elsevier B.V. All rights reserved.