M.Tokitani 2) , H. Iwakiri 1) , N. Yoshida 1) , S. Masuzaki 2) , N. Ashikawa 2)

1. 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. 2008

2. I‐loop formation He ion, atom Annihilation? Aggregation of I Bombarding plasma facing components with helium causes changing of their properties • He ash: divertor • He GDC: divertor & first wall • CX neutral: divertor & first wall 10th ITPA conference, Avila, 7-10 Jan. 2008

3. Effects of pre-irradiation of helium 8keV,1ｘ1021D2+/m2 @300K 21 + 2 8x10 He /m W 21 + 2 2x10 He /m 20 + 2 1x10 He /m s) no He irr. 2 /m 2 18 1x10 3.5 Desorption Rate (D 17 8x10 3.0 17 2.5 6x10 18 4.0x10 8keV, 2ｘ1021He+/m2 ＠300K + 2 1x1022D /m 2.0 2 17 s) 4x10 4x1021 2 /m 1.5 1x1021 2 17 2x10 5x1020 1.0 No He 1x1022 0 300 400 500 600 700 800 Desorption Rate (D 900 0.5 0.0 300 400 500 600 700 800 900 Temperature (K) • 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. 10th ITPA conference, Avila, 7-10 Jan. 2008

4. 20nm 20nm Specimens surfaces analysis after exposed to three glow discharges (TEM) He-GD Ne-GD Un-irradiation H-GD Bright field images Dark field images • Incident energy of ions are 200-300eV, 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. 2008

5. Depth distribution of He bubbles 10nm Stainless steel specimen (SUS316L) Cross-sectional TEM observation by using FIB technique after He-GDC Stereoscopic observation by TEM He a) LHD He-GDC (200eV，65h) (1) (2) TRIM-91(200eV-He+) He concentration [a.u.] b) He+ irra. exp. (2keV-He+,1.0x1022) (1) Deposition layer with about 10nm thick, very heavy damage such as large bubbles formation and surface roughening. TRIM-91(2keV-He+) (2) In bulk, about 30nm thick, small helium bubbles (1-2nm) were formed in the matrix. 0 10 20 30 40 50 Depth [nm] By using He-GDC, serious irradiation defects are formed in the deep range. 10th ITPA conference, Avila, 7-10 Jan. 2008

6. Un-exposed surface Exposed surface 10 [nm] 653 550 mm 0 0 10nm mm 0 10 The feature of Ne-GDC Surface erosion of SUS316L after Ne-GDC as observed by AFM Cross-sectional TEM observation by using FIB technique after Ne-GDC (b) Ne-GDC Ne • 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. 2008

7. Retention of Deuterium after GDCs 2keV-D+ Room temp. 1.0x1022[D+/m2] • 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. SUS316L • He-GDC(65h) • H-GDC(71.5h) • Ne-GDC(55h) 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. 10th ITPA conference, Avila, 7-10 Jan. 2008

8. Mechanism of retention modification by He irradiation Blistering suppression by simultaneous H and He ion beam irradiation 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. 10th ITPA conference, Avila, 7-10 Jan. 2008

9. 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. Range of hydrogen isotopes Damaged region diffusion 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. 2008

10. 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 10th ITPA conference, Avila, 7-10 Jan. 2008