Deuterium trapping in tungsten damaged by highenergy hydrogen ion irradiation

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/Wdpa
• Similar to 800 MeV p damage
• 0.01 traps/Wdpa
• 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 gt 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.

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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 gt 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.

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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
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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 distribution simulated by TMAP7

• Simulation conditions
• Trap energy1.34eV(vacancies)
• 2.1eV (voids)
• Diffusion coeff. Fraunfelders
• Trapping rate
• De-trapping rate
• Distribution TRIM-88
• Trap density
• 0.014 traps/Wdpa
• 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.

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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)