Effect of noble gas ion pre-irradiation on deuterium retention in tungsten

Abstract

Impurity seeding of noble gases is an effective way of decreasing the heat loads onto the divertor targets in fusion devices. To investigate effect of noble gases on deuterium retention, tungsten targets have been implanted by different noble gas ions and subsequently exposed to deuterium plasma. Irradiation induced defects and deuterium retention in tungsten targets have been characterized by positron annihilation Doppler broadening and thermal desorption spectroscopy. Similar defect distributions are observed in tungsten irradiated by neon and argon, while it is comparatively low in the case of helium. The influence of helium pre-irradiation on deuterium trapping is found to be small based on the desorption spectrum compared with that of the pristine one. Neon and argon pre-irradiation leads to an enhancement of deuterium trapping during plasma exposure. The influence on deuterium retention is found to be argon > neon > helium when comparing at a similar crystal damage level.

Significant growth of vacancy-type defects by post-irradiation annealing in neon ion-irradiated tungsten probed by a slow positron beam

“…The ion and vacancy distributions in tungsten were calculated with a displacement threshold energy of 90 eV [17,21] using the SRIM-2013 code [22,23]. The incident positron distributions P (z) were calculated by using a formula called the Makhovian distribution [24],…”

“…Positron annihilation spectroscopy is a powerful probe for investigating vacancy-type defects in crystalline materials [10,11,12], and several defect studies in protonor He + -irradiated tungsten have been performed using positrons [13,14,15,16]. However, few studies on the defects in noble gas ion-irradiated tungsten using positrons have been reported [17,18], except for He + -irradiation. Irradiation of the other noble gases which represent heavier particles can cause more significant damage to tungsten.…”

Evolution of surface morphology and helium bubble in tungsten under 40 keV helium ions implantation followed by deuterium plasma exposure

“…In the case of ion irradiation, Cheng et al [5] used 20 keV He ion to damage W then studied the D retention in these samples and found that the presence of He only slightly inhibited the D retention in W. Researchers believed that He atoms could occupy vacancies and led to the reduction of nucleation sites for D atoms. As opposed to Cheng et al, Markelj et al [6] and Iwakiri et al [7] reported that the presence of He could enhance the D retention in W. Both Markelj et al and Iwakiri et al [7] found that the dislocations and vacancies induced by He ions pre-implantation acted as the D trapping sites.…”