10th ITPA conference, Avila, 7-10 Jan Changes of Deuterium Retention Properties on Metals due to the Helium Irradiation or Impurity Deposition M.Tokitani 2), H. Iwakiri 1), N. Yoshida 1), S. Masuzaki 2), N. Ashikawa 2) 1) Kyushu University 2) National Insititute for Fusion Science

10th ITPA conference, Avila, 7-10 Jan Bombarding plasma facing components with helium causes changing of their properties He ash: divertor He GDC: divertor & first wall CX neutral: divertor & first wall Aggregation of I I ‐ loop formation He ion, atom Annihilation?

10th ITPA conference, Avila, 7-10 Jan Effects of pre- irradiation of helium Increase of helium bubble and dislocation loops densities causes increase of strongly trapped deuterium retention. In a fixed helium bubble and dislocation loops densities case, deuterium trapping sites are changed depending on D fluence. Lower fluence ： strongly trapped Higher fluence ： strong trap sites are filled, and weakly trapped D increase x x10 22 D 2 + /m 2 4x x x10 20 No He 1x10 22 Temperature (K) Desorption Rate (D 2 /m 2 s) x x x x x x10 21 He + /m 2 2x10 21 He + /m 2 1x10 20 He + /m 2 no He irr. Desorption Rate (D 2 /m 2 s) W 8keV,1 ｘ D 2 + /m 8keV, 2 ｘ He + /m 2 ＠ 300K

10th ITPA conference, Avila, 7-10 Jan Bright field images Ne-GD H-GD He-GD Un-irradiation Dark field images 20nm Specimens surfaces analysis after exposed to three glow discharges (TEM) Incident energy of ions are eV, and temperature of specimens were almost room temperature. In contrast with the very heavy damages observed in the case of He-GD, these defects were not observed in the case of H-GD and Ne-GD.

10th ITPA conference, Avila, 7-10 Jan Depth distribution of He bubbles He concentration [a.u.] a) LHD He-GDC (200eV ， 65h) Depth [nm] b) He + irra. exp. (2keV-He +,1.0x10 22 ) TRIM-91(2keV-He + ) TRIM-91(200eV-He + ) Cross-sectional TEM observation by using FIB technique after He-GDC Stereoscopic observation by TEM 10nm He (1) (2) (1) Deposition layer with about 10nm thick, very heavy damage such as large bubbles formation and surface roughening. (2) In bulk, about 30nm thick, small helium bubbles (1-2nm) were formed in the matrix. By using He-GDC, serious irradiation defects are formed in the deep range. Stainless steel specimen (SUS316L)

10th ITPA conference, Avila, 7-10 Jan Un-exposed surface Exposed surface mm mm [nm] The feature of Ne-GDC (b) Ne-GDC 10nm Ne Surface erosion of SUS316L after Ne-GDC as observed by AFM Cross-sectional TEM observation by using FIB technique after Ne-GDC Ne-GDC can remove the surface efficiently by a high sputtering yield. A smooth surface and a no-defects internal structure can be obtained by using Ne-GDC.

10th ITPA conference, Avila, 7-10 Jan  He-GDC(65h)  H-GDC(71.5h)  Ne-GDC(55h) Retention of Deuterium after GDCs Additional deuterium irradiation to the specimen pre-exposed to three GDC were conducted in order to confirm the change of deuterium retention properties due to the GDCs. Fresh specimen (irradiated only D + ) Total retention of deuterium becomes lower by performing GDCs. ►Reduction of oxidized film. He-GDC showed highest deuterium retention among the three GDCs. Ne-GDC showed lowest deuterium retention. In H-GDC, most of the retained deuterium desorbs up to 370K. SUS316L 2keV-D + 1.0x10 22 [D + /m 2 ] Room temp.

10th ITPA conference, Avila, 7-10 Jan Y. Ueda reported in ICFRM 2007 that: Only 0.1% of He strongly affects H inward diffusion in W. Stress field around bubbles and reduction of effective diffusion area (diffusion through bubbles is unlikely) could reduce H diffusion. In Ueda’s experiment, incident energy of deuterium and helium is 0.33keV and 1keV, respectively. In LHD glow discharge case, incident energy of deuterium and helium are 2keV and 200eV (glow discharge), respectively. The difference of ranges of hydrogen isotopes and helium could be a key parameter. Blistering suppression by simultaneous H and He ion beam irradiation Mechanism of retention modification by He irradiation

10th ITPA conference, Avila, 7-10 Jan Possible mechanism for the change of hydrogen isotope retention properties Stress field caused by bubbles and displacements and/or reduction of diffusion area could reduce hydrogen isotope transport in bulk. Damaged region Range of hydrogen isotopes diffusion Deposition layer on the surface also a possible mechanism for reduction of hydrogen isotope release from the surface

10th ITPA conference, Avila, 7-10 Jan Summary Hydrogen isotope retention properties in metal are changed by helium irradiation. –Increase of hydrogen isotope retention is observed after helium ion beam (8 keV) irradiation. –The influence of the GDCs on the deuterium retention was also examined. The sample exposed to He-GDC showed highest deuterium retention while Ne-GDC showed lowest. Stress field caused by bubbles and displacements and/or reduction of diffusion area due to helium irradiation could be a barrier for hydrogen isotope transport. –Difference of ranges of hydrogen isotope and helium could be a key parameter. Estimation of incident He energy (ash, CX) is necessary –Systematic experiment is necessary to confirm this assumption. Material, temperature, and so on After neon glow discharge, there is almost no damage in sample, and hydrogen retention substantially decreases. –Neon glow discharge can be a tool for wall conditioning in ITER