Study of thermal hydrogen atom interaction with undamaged and self-damaged tungsten S. Markelj a,⇑,1 , O.V. Ogorodnikova b , P. Pelicon a , T. Schwarz-Selinger b , K. Sugiyama b , I. C ˇ adez ˇ a a Joz ˇef Stefan Institute and Association EURATOM-MHEST, Jamova cesta 39, 1000 Ljubljana, Slovenia b Max-Planck-Institut für Plasmaphysik EURATOM Association, Boltzmannstr. 2, D-85748 Garching, Germany article info Article history: Available online 18 January 2013 abstract Retention of deuterium in undamaged and damaged polycrystalline tungsten exposed to thermal D beam was studied between 370 K and 500 K as a function of D fluence. Damaged samples were produced by W ion irradiation with damage concentration upto 0.89 displacements per atom. ERDA was used to follow near-surface H and D areal densities in situ during the exposure and the D depth profiles down to 6 lm were extracted ex situ by NRA. Both methods give the same D concentration within the first 400 nm. D retention in undamaged and damaged W exposed to thermal (0.2 eV) atoms was observed for the first time. Retention in damaged W is found to be higher than in undamaged due to additional traps created by heavy W ion pre-irradiation. Isotope exchange at the surface and in the bulk of damaged W was also investigated in situ by ERDA at different sample temperatures. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Prediction of hydrogen isotope recycling and retention in tung- sten is an important issue due to plasma performance and the safety limitations of tritium inventory in future fusion reactors [1]. Besides being exposed to fusion fuel (deuterium and tritium), the plasma facing components of fusion reactors will be exposed also to 14 MeV neutrons and He from fusion reaction. The com- bined effects of n-irradiation and incorporation of helium and hydrogen isotopes will affect the properties of plasma-facing mate- rial. The damage generated by n-irradiation modifies the thermo- mechanical properties of the material, fuel retention, surface sput- tering, etc. [1,2]. Experimental data on the influence of displace- ment damage on hydrogen accumulation and recycling in materials are very scarce and the theoretical understanding of hydrogen transport through damaged material is also incomplete. D retention in damaged tungsten, exposed to energetic particle bombardment by D ions or plasmas for different energies, fluxes and fluence, was investigated by several groups [2–7]. It was shown that retention in damaged W is higher compared to undam- aged one. Retention of deuterium in damaged tungsten exposed to neutral thermal atoms was not addressed so far. However, while magnetically confined ions will only interact with surfaces in the close proximity of the plasma, neutral hydrogen atoms will reach any surface inside the vessel after multiple collisions. This can lead to significant contribution of retained hydrogen in the remote areas to the overall fuel balance. The purpose of this work is there- fore to study the influence of radiation damage on hydrogenic retention in tungsten exposed to thermal hydrogen atoms. The damage is produced by implantation of high energy W ions (upto 0.89 dpa), which is the most appropriate approach for simulating n-irradiation. Heavy ion irradiation of a material generates a dense cascade with large clusters, which are typical for n-irradiation. Self-implantation (W in W) assures that chemical effects are avoided. 2. Experiment The D retention and recycling in polycrystalline tungsten was studied in situ by ion beam method ERDA (Elastic Recoil Detection Analysis) [8]. A 4.3 MeV 7 Li 2+ was used as the probing ion beam for these measurements performed at the 2 MV tandem accelerator at the Joz ˇef Stefan Institute (JSI), Ljubljana. The experimental config- uration of the set-up is shown in Fig. 1. More details can be found in [9]. The ERDA method is one of the rare techniques which enable simultaneous hydrogen and deuterium depth profiling. During the experiment ERDA spectra were recorded with typical doses of 1.7 lC and 3.42 lC, providing the time variation of areal density of adsorbed H and D on the surface, so-called H and D surface areal densities. They were obtained by integrating the surface peaks, having depth resolution of around 10 nm. The integrated areas for the H and D surface peaks are marked in Fig. 2 as H S and D S respectively, where typical ERDA spectra are presented. The signal appearing at energies below the H and D surface peaks is due to H or D in ‘‘bulk’’, respectively, also marked in Fig. 2, reaching upto 400 nm below tungsten surface. The errors for the ‘‘bulk’’ concen- 0022-3115/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2013.01.224 ⇑ Corresponding author. E-mail address: sabina.markelj@ijs.si (S. Markelj). 1 Presenting author. Journal of Nuclear Materials 438 (2013) S1027–S1031 Contents lists available at SciVerse ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat