Search

Tungsten (W) samples were damaged by neutron and 6.4 MeV Fe-ion irradiation above 1000 K simulating the divertor operation temperature. Deuterium (D) retention properties were examined by decorating the damaged W with D and subsequent thermal desorption spectroscopy (TDS) measurements. Vacancy clusters were the major D trapping site in the W irradiated with Fe-ion at 873 K, although D retention by vacancy clusters decreased in the W irradiated with Fe-ion at 1173 K due to dynamic annealing. The D de-trapping activation energy from vacancy clusters was found to be 1.85 eV. D retention in neutron damage W was larger than that damaged by Fe-ion due to the uniform distribution of irradiation defects. The D desorption behaviors from neutron damaged W was simulated well by assuming the D de-trapping activation energy to be 1.52 eV. [ABSTRACT FROM AUTHOR]

Deuterium retention behavior in tungsten damaged by fast neutrons at high temperatures (0.43 dpa at 918 K and 0.74 dpa at 1079 K) and 6.4 MeV Fe2+ (0.3 dpa at R.T.) were investigated to evaluate the tritium retention property of fusion reactor divertors. A deuterium gas absorption method was carried out to avoid additional damage that may be induced by plasma exposure, then, deuterium retention and desorption behaviors were investigated quantitatively by means of thermal desorption spectroscopy and the following simulation code. The deuterium desorption spectra for tungsten samples were analyzed by the numerical code which includes the elementary steps of hydrogen isotope migration processes including diffusion, trapping, detrapping, and surface recombination. The evaluated deuterium detrapping energy from the irradiation defects in neutron irradiated tungsten sample was larger than that in 6.4 MeV Fe2+ irradiated tungsten. It was suggested that the dominant deuterium trapping site in the neutron irradiated tungsten would be voids which was formed by the accumulation of vacancies during neutron irradiation under high temperature and long duration. [ABSTRACT FROM AUTHOR]

• Hydrogen (H) and deuterium (D) permeation fluxes for tungsten (W) by H-D mixed plasma were studied to clarify the hydrogen isotope effect on permeation by newly designed plasma driven permeation (PDP) device. • When single species of h or d was irradiated, the h permeation rate showed approximately 1.6 times as high as that of d. • H and d permeation fluxes were clearly reduced by seeding he in H-D mixed plasma. At lower temperature (∼723 K), the ratio of steady permeation fluxes of h and d was about 75 : 25, confirming the high permeation flux of h. • H and d permeation fluxes were reached almost unity at 923 K. Hydrogen (H) and deuterium (D) permeation fluxes for tungsten (W) by H-D mixed plasma were studied to clarify the hydrogen isotope effect on permeation by a newly designed plasma driven permeation (PDP) device at Shizuoka University. A mixed H-D plasma was produced by introducing H and D gasses with various ratios. The atomic ratio and permeation flux in the plasma were measured during the experiments. It was found that the H:D atomic ratio in the plasma was almost proportional to the introduced H:D gas ratio. When single species of H or D was irradiated, the H permeation rate showed approximately 1.6 times as high as that of D. Under H-D mixed plasma irradiation, the highest HD permeation rate was observed when the atomic ratio of H:D in the plasma was 50:50. In addition, the effect of He seeding on H-D mixed plasma driven permeation behavior was also evaluated. The recycling of hydrogen isotopes on the upstream side was enhanced due to the formation of He bubbles near the surface, which would prevent the dissolution of hydrogen isotopes into bulk W and enhance the reflection process during plasma exposure. H and D permeation fluxes were clearly reduced by seeding He in H-D mixed plasma. At lower temperature (∼723 K), the ratio of steady permeation fluxes of H and D was about 75 : 25, confirming the high permeation flux of H. These results have demonstrated a significant hydrogen isotope effect, even if He was seeded or not. As the temperature increased, H and D permeation fluxes approached unity at 923 K. This indicates that the hydrogen isotope effect was determined by the combination of recycling / reflection at or beneath the surface, which will be controlled by the temperature during plasma exposure. [ABSTRACT FROM AUTHOR]

Abstract Deuterium (D) retention behaviors for the 3 keV Helium (He+) implanted damaged-Tungsten (W) and 10 keV Carbon (C+) - 3 keV He+ simultaneous implanted damaged-W were evaluated by thermal desorption spectroscopy (TDS) to understand the synergetic effect of defect formation and C/He existence on D retention behavior for W with various damage level. For the He+ implantation, the retention of D trapped by dislocation loops was controlled by 3 keV He+ fluence. The D retention in the deeper region was reduced by He+ implantation with higher He+ fluence due to the formation of He bubbles and dense defects at the surface region which would reduce the effective D diffusion coefficient. In addition, in the case of the simultaneous C+ - He+ implantation, the reduction of D retention trapped in the deeper region was also found by the higher C+ - He+ fluence. It can be said that D retention behavior was controlled by the formation of He induced defects and accumulation of He near the surface even if the damages were introduced in the deeper region. [ABSTRACT FROM AUTHOR]