9 th International Workshop on Hydrogen Isotopes in Fusion Reactor Materials Salamanca, Spain, June 2 - 3, Simulation experiments on neutron damage of tungsten M. Fukumoto, H. Kashiwagi, Y. Ohtsuka, Y. Ueda Graduate School of Engineering, Osaka University M. Taniguchi, T. Inoue, K. Sakamoto, J. Yagyu, T. Arai Japan Atomic Energy Agency I. Takagi Graduate School of Engineering, Kyoto University T. Kawamura, N. Yoshida Interdisciplinary Graduate School of Engineering Sciences, Kyushu University

2 Purpose of this study & Outline of this talk Purpose of this study  Investigation of hydrogen isotope behavior in damaged W Outline of this talk  Blister formation Effects of radiation damage on blister formation  Deuterium retention D concentration in damaged W Effects of annealing on D retention TDS profiles as a function of fluence Preliminary TMAP7 simulation

3 Experimental sequence W samples  Hot rolled and stress relived  Mirror-polished less than 0.01  m roughness 1.Damage Creation  Ion energy: 300 and 700 keV H -  Pulse duration: 1 s every 60 s (~1000 shots)  Temperature: below 473 K (to avoid recovery of defects) 2.H-C irradiation  Ion energy: 1.0 keV (include H +, H 2 +, and H 3 + )  Fluence: 7.5 x H + /m 2  Carbon: ~0.8 %  Temperature: 473 K 3.SEM observation 2.D implantation  Ion energy: 1.0 keV (include D +, D 2 +, and D 3 + )  Fluence: 0.5 x ~ 8.0 x D + /m 2  Temperature: 473 K 3.SIMS/NRA measurements  NRA was used for absolute calibration 4.TDS measurements  1 K/s, R.T. ~ 1100 K Blister formation D depth distribution D desorption 1.5.Annealing  673 K, 1 h  1173 K, 1 h

4 Effects of radiation damage on blister formation The number of blisters was decreased with increasing radiation damage  The blisters with diameter of 20  m or less was decreased （ a ） 0dpa （ b ） 0.3dpa （ c ） 3.5dpa 20  m Fluence: 7.5 x H + /m 2 Temp.: 473 K Carbon: ~0.8 %

5 Mechanism of blister formation trapped at grain boundaries →blister formation Undamaged W700keV H - damaged W decrease of H trapped at grain boundaries damaged zone ~1.5  m H was not accumulate at the grain boundaries within radiation damage  Small blisters (<20  m) were decreased Large blisters were formed since radiation damage was not produced

6 D distribution as a function of fluence (473 K) D conc. near surface was saturated at ~5.0x10 23 D + /m 2  D conc.: ~0.9x10 27 D/m 3  Trap density traps/W  Production rate traps/W·dpa  Similar to 800 MeV p damage* ~0.01 traps/W·dpa D conc. at ~1.0 µm was not saturated up to 8.0x10 24 D + /m 2 * B.M. Oliver et al., J. Nucl. Mater (2002) Fluence: 0.5 ~ 8.0 x D + /m 2 Temp.: 473 K Damage: ~4.8 dpa

7 Effects of 673 K annealing on D trapping D concentration was decreased by annealing at 673 K for 1 h.  Change of surface density 0.8x10 27 => 0.6x10 27 D/m 2  ~20 % reduction Most of self-interstitials could be eliminated*.  Vacancy type defects are still remained. * M. J. Attard et al., Phys. Rev. Lett., 19, (1967) 73. Fluence: 5.0 x D + /m 2 Temp.: 473 K Damage: ~4.9 dpa

8 Effects of 1173 K annealing on D trapping D conc. was also decreased by annealing at 1173K for 1h.  Change of surface density 0.9x10 27 => 0.2x10 27 D + /m 2  ~80 % reduction (near surface) Single vacancies could be annealed by this heat treatment*  Voids formation could be still take place** * D. Jeannotte et al., Phys. Rev. Lett., 19, (1967) 232. ** H. Eleveld et al., J.N.M., , (1994) Fluence: 5.0 x D + /m 2 Temp.: 473 K Damage: ~4.4 dpa

9 TDS spectra of two samples Fitted by Gaussian functions.  Peak 1: ~770 K  Peak 2: ~860 K  Peak 3: ~920 K Fluence: 5.0 x D + /m 2 Temp.: 473 K Undamaged W~4.8 dpa damaged W Damaged W has much higher D desorption

10 Fluence dependence of each peak Damaged samples  Peak 1 (~770 K) one order of magnitude higher than undamaged sample increased with fluence  Peak 2 (~860 K) same as undamaged sample constant with fluence  Peak 3 (~920 K) only damaged samples increased with fluence D was trapped at the vacancies (Peak 1) and voids (Peak 3) Fluence: 0.5 ~ 8.0 x D + /m 2 Temp.: 473 K Damage: ~4.8 dpa

11 D distribution as a function of fluence (673 K) In the case of 673 K implantation, trapping and annealing of damage were simultaneously took place Radiation damage around ~1.1  m could be annealed during implantation Fluence: 0.5 ~ 5.0 x D + /m 2 Temp.: 673 K Damage: ~3.2 dpa

12 D distribution simulated by TMAP7 Simulation conditions  Trap energy: 1.34eV(vacancies)* 2.1eV (voids)*  Diffusion coeff.: Fraunfelder’s  Trapping rate:  De-trapping rate:  Distribution: TRIM-88  Trap density: traps/W·dpa  Other conditions: same as exp. D trapping proceeds from surface trapping sites All trap sites were filled less than 6.0 x D + /m 2  Much lower than exp. results (8.0 x D + /m 2 )  TMAP7 results did not agree with exp. results *M. Poon et al., JNM, 374 (2008) 390. D Concentration (x10 27 D/m 3 )

13 Conclusion Blister Formation  Hydrogen isotopes were not accumulate at the grain boundaries within damaged zone Deuterium depth profiles  D conc. near surface was saturated at the fluence of 5.0 x D + /m 2 D conc. near surface was 0.9 x D/m 3 Damage production rate was similar to 800 MeV p irradiated W  D conc. at ~1.0  m was increased but not saturated up to the fluece of 8.0 x D + /m 2  Preliminary TMAP7 simulation did not reproduce exp. Results TDS measurements  D was trapped at the vacancies and voids produced with high-energy ion irradiation

14 Experimental sequence 1.Damage Creation  Ion energy: 300 and 700 keV H -  Pulse duration: 1 s every 60 s (~1000 shots)  Temperature: below 473 K (to avoid recovery of defects) 2.H-C irradiation  Ion energy: 1.0 keV (include H +, H 2 +, and H 3 + )  Fluence: 7.5 x H + /m 2  Carbon: ~0.8 %  Temperature: 473 K 3.SEM observation W samples  Hot rolled and stress relived  at%  Mirror-polished less than 0.01  m roughness 2.D implantation  Ion energy: 1.0 keV (include D +, D 2 +, and D 3 + )  Fluence: 0.5 x ~ 8.0 x D + /m 2  Temperature: 473 K 3.SIMS/NRA measurements  NRA was used for absolute calibration 4.TDS measurements  1 K/s, R.T. ~ 1100 K

15 Outline of this talk Background and Purpose of this study Experimental sequence Experimental results  Blister formation Effect of radiation damage on blister formation  Deuterium retention D concentration in damaged W Effects of annealing on D retention TDS profiles as a function of incident fluence Preliminary TMAP7 simulation Conclusion

16 Background and Purpose of this study Background of this study  In ITER, W is a candidate PFM for diverter region Extensive studies have been made for “undamaged” W  In DT fusion phase, fast neutrons are generated W is simultaneously irradiated by hydrogen isotopes and neutrons Interaction between radiation-induced defects and hydrogen isotope in W materials is very important  Trapping, release, and diffusion in damaged W are not clear Purpose of this study  Investigation of surface morphology and deuterium behavior in damaged W Blistering, D depth distribution and desorption characteristics

17 A blister with diameter of 25  m had a blister gap at 5  m in depth. A large blister with diameter of approximately 100  m had a blister gap at 10  m in depth. A.A. Haasz et al.: The effect of ion damage on deuterium trapping in tungsten, J. Nucl Mat., , pp (1999). 5  m 10  m Relationship between blister diameter and depth of blister gaps 25  m 100  m

18 ブリスタの直径と亀裂深さの関係 ~ 1.5  m ~ 5.5  m 0 dpa 300keV,700keV H - による照射損傷 で、深さ 1.5  m 付近の亀裂が減少  300keV H - : 損傷の範囲より深い  700keV H - : 損傷の範囲内 300keV, 3.7dpa 照射損傷により減少 するブリスタ直径 照射損傷でも減少 しないブリスタ直 径 ~ 1.0  m

19 Effect of damaged zone on blister formation The blisters less than 20  m in diameter were decreased with an increase in damaged zone  300keV H - ： decrease of small blisters was low  700keV H - ： small blisters were suppressed （ a ） 0dpa （ b ） 300 keV, 3.7 dpa （ c ） 700 keV, 3.5dpa 20  m Fluence: 7.5 x H + /m 2 Temp.: 473 K Carbon: ~0.8 %