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Deuterium trapping in tungsten damaged by high-energy hydrogen ion irradiation

Deuterium trapping in tungsten damaged by high-energy hydrogen ion irradiation. 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

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Deuterium trapping in tungsten damaged by high-energy hydrogen ion irradiation

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  1. Deuterium trapping in tungsten damaged by high-energy hydrogen ion irradiation 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. Outline of this talk • Background and Purpose of this study • Experimental sequence • Experimental results • D concentration in damaged W • Effects of annealing on D retention • TDS profiles as a function of incident fluence • Preliminary TMAP7 simulation • Conclusion

  3. 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 deuterium behavior in damaged W • D depth distribution and desorption characteristics

  4. Experimental sequence • Damage Creation • Ion energy: 300 keV H- • Pulse duration: 1 s every 60 s (~1000 shots) • Temperature: below 473 K (to avoid recovery of defects) • D implantation • Ion energy: 1.0 keV (D+, D2+, and D3+ were contained) • Fluence: 0.5 x 1024 ~ 8.0 x 1024 D+/m2 • Temperature: 473 K • SIMS/NRA measurements • NRA was used for absolute calibration • TDS measurements • 1 K/s, R.T. ~ 1100 K • W samples • Hot rolled and stress relived • Mirror-polished less than 0.01 mm roughness

  5. D distribution as a function of fluence • Fluence: 0.5 ~ 8.0 x 1024 D+/m2 • Temp.: 473 K • Damage: ~4.8 dpa • D conc. near surface was saturated at ~5.0x1023 D+/m2 • D conc.: ~0.9x1027 D/m3 • Trap density • 0.014 traps/W • Production rate • 0.014 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 8.0x1024 D+/m2 * B.M. Oliver et al., J. Nucl. Mater. 307-311 (2002) 1418.

  6. Effects of 673 K annealing on D trapping • Fluence: 5.0 x 1024 D+/m2 • Temp.: 473 K • Damage: ~4.9 dpa • D concentration was decreased by annealing at 673 K for 1 h. • Change of surface density 0.8x1027 => 0.6x1027 D/m2 • ~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.

  7. Effects of 1173 K annealing on D trapping • Fluence: 5.0 x 1023 D+/m2 • Temp.: 473 K • Damage: ~4.4 dpa • D conc. was also decreased by annealing at 1173K for 1h. • Change of surface density 0.9x1027 => 0.2x1027 D+/m2 • ~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., 212-215, (1994) 1421.

  8. TDS spectra of two samples • Fluence: 5.0 x 1024 D+/m2 • Temp.: 473 K • Fitted by Gaussian functions. • Peak 1: ~770 K • Peak 2: ~860 K • Peak 3: ~920 K • Damaged W has much higher D desorption Undamaged W ~4.8 dpa damaged W

  9. Fluence dependence of each peak • Fluence: 0.5 ~ 8.0 x 1024 D+/m2 • Temp.: 473 K • Damage: ~4.8 dpa • 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 defects related to Peak 1 (~770 K) and Peak 3 (~920 K)

  10. D Concentration (x1027 D/m3) 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: 0.014 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 1022 D+/m2 • Much lower than exp. results (8.0 x 1024 D+/m2) • TMAP7 results did not agree with exp. results *M. Poon et al., JNM, 374 (2008) 390.

  11. Conclusion • Deuterium depth profiles • D conc. near surface was saturated at 5.0x1023 D+/m2 • Damage production rate was similar to 800 MeV p irradiated W • D conc. at ~1.0 mm was increased but not saturated up to 8.0x1024 D+/m2 • Preliminary TMAP7 simulation did not reproduce exp. results • Effect of annealing • Annealing at 673 K for 1 h decreased D retention by ~20 % • Annealing at 1173 K for 1 h decreased D retention by ~80 % • TDS measurements • D was trapped at the radiation induced defects associated with Peak 1 (~770 K) and Peak 3 (~920 K)

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