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• Alleviation of impurities levels in Li for IFMIF-type neutron source are suggested. • No fatal problems are found by applying the alleviation of impurities levels. • Level of Be-7 in Li under process can be diminished by the alleviation. The alleviated limits of impurities of nitrogen and hydrogen isotopes in lithium are suggested to be 400wppm and 550appm, respectively for early realization of Advanced Fusion Neutron Source planned in Japan. The applicability of the suggestion is discussed by comparing to that of IFMIF. As the results, not less than 4-year buffer for R&D of nitrogen trap are brought in, which is thought as one of bottle neck. Additionally, the application of this suggestion would diminish the beryllium (a radioactive isotope will generate in A-FNS process) concentration in processing lithium, as well. On the other hand, it is indicated that there would be no fatal problems by application of the present suggestion. [ABSTRACT FROM AUTHOR]

Abstract: Retention of hydrogen isotopes in the carbon (isotropic graphite) first wall tiles of JT-60U was studied by secondary ion mass spectrometry and thermal desorption spectroscopy. The surface morphology and erosion/deposition profiles of the tiles were characterized using scanning electron microscope and X-ray photoelectron spectroscopy. The upper area is mainly eroded, while the bottom area of the inboard wall is dominated by deposition. In contrast to the divertor area, hydrogen isotope retention in the eroded wall area was generally larger than that in the deposition dominated area. Measured near surface concentrations of hydrogen isotopes in the wall tiles, as well as the D/H ratios, were a little higher than those in the divertor area. This indicates direct implantation of high-energy D from NBI into the first wall. The lower temperature of the first wall relative to the divertor tiles would reduce desorption and/or replacement of implanted D by subsequent D or H impingement. [Copyright &y& Elsevier]

Abstract: TDS analyses have been performed in order to examine helium irradiation effects for deuterium retention in boron coating films prepared by PACVD. It is clarified that the deuterium retention is reduced due to the irradiation prior to deuterium. There is no correlation between the retention variations of deuterium and helium, and thus the helium occupation seems hardly to contribute to the reduction. The third peaks in the TDS spectra shift on the high temperature side with the irradiation fluence. It is presumed that helium irradiation forms certain layers by knocking on boron atoms, in which deuterium retention is partly restricted, and trapped deuterium needs higher energy for the desorption. [Copyright &y& Elsevier]

Micro-/nano-characterization of the surface structures on the divertor tiles used in the first campaign (2011–2012) of the JET tokamak with the ITER-like wall (JET ILW) were studied. The analyzed tiles were a single poloidal section of the tile numbers of 1, 3 and 4, i.e., upper, vertical and horizontal targets, respectively. A sample from the apron of Tile 1 was deposition-dominated. Stratified mixed-material layers composed of Be, W, Ni, O and C were deposited on the original W-coating. Their total thickness was ∼1.5 μm. By means of transmission electron microscopy, nano-size bubble-like structures with a size of more than 100 nm were identified in that layer. They could be related to deuterium retention in the layer dominated by Be. The surface microstructure of the sample from Tile 4 also showed deposition: a stratified mixed-material layer with the total thickness of 200–300 nm. The electron diffraction pattern obtained with transmission electron microscope indicated Be was included in the layer. No bubble-like structures have been identified. The surface of Tile 3, originally coated by Mo, was identified as the erosion zone. This is consistent with the fact that the strike point was often located on that tile during the plasma operation. The study revealed the micro- and nano-scale modification of the inner tile surface of the JET ILW. In particular, a complex mixed-material deposition layer could affect hydrogen isotope retention and dust formation. [ABSTRACT FROM AUTHOR]

Surface morphology changes and deuterium (D) retention in Toughened, Fine-Grained Recrystallized Tungsten (TFGR W) with TaC dispersoids (W-TaC) and pure tungsten exposed to D plasmas to a fluence of 10 26 D/m 2 s were studied as a function of the D ion flux (10 22 –10 24 D/m 2 s). As the flux increased from 10 22 D/m 2 s to 10 24 D/m 2 s, the numbers of blisters increased for both materials. However, smaller blisters were observed on W-TaC compared to pure W. In W-TaC, cracks beneath the surface along grain boundaries were observed, which were comparable to the blister sizes. The reason for the smaller blister sizes may arise from smaller grain sizes of W-TaC. In addition, reduction of the D retention in W-TaC was observed for higher flux exposures. D depth profiles indicate this reduction arises due to decrease in trapping in the bulk. [ABSTRACT FROM AUTHOR]

Surface topography and deuterium retention in polycrystalline hot-rolled W and W–5%Re have been examined after exposure to a low-energy (76 eV), high flux (around 10 22 D/m 2 s) deuterium plasma to an ion fluence of 10 26 D/m 2 at various temperatures. The methods used were confocal laser scanning microscopy and the D( 3 He, p) 4 He nuclear reaction at 3 He energies varied from 0.69 to 4.0 MeV. During exposure to the D plasma at temperatures in the range from 348 to 673 K, small blisters of size in the range from about 1 to about 15 μm, depending on the exposure temperature, are formed on the W and W–5%Re surfaces. In the W–5%Re, the deuterium retention demonstrates its maximum at exposure temperature of 463 K, while in the W this maximum is shifted to 523 K. A difference in the temperature dependence of the D retention for the W and W–5%Re is explained, as a rough approximation, by temperature dependences of the ductility of these materials. [ABSTRACT FROM AUTHOR]

Abstract: Dependence of implantation temperature on chemical behavior of energetic deuterium implanted into WC was investigated by TDS and XPS. 1.0keV ions were implanted into WC samples at the implantation temperature range of 323–873K. It was found that the deuterium retention decreased as the implantation temperature increased. Above 573K, most of the retained deuterium was bound to C, which was less than 20% of the total D retention after implantation at 323K. Above 673K, C was segregated on the WC surface and some of the implanted deuterium was retained in the segregated carbon layer. Additionally, it can be said that the D retention in WC was much less than that in other carbon-related materials, such as graphite and SiC. Hydrogen isotope retention can be reduced significantly when WC is formed on a divertor surface as a redeposited layer. [Copyright &y& Elsevier]

Abstract: Deuterium (D) and Hydrogen (H) retention in carbon tiles exposed to DD and HH discharges in the JT-60U W-shaped divertor has been investigated by means of thermal desorption spectroscopy (TDS) and secondary ion mass spectrometry (SIMS). In the thick re-deposited layers on the outer divertor, hydrogen (H+D) was retained rather homogeneously with its concentration of 0.03 in (D+H)/C atomic ratio, which is attributed to the surface temperature rise above 900K. Owing to the HH discharges performed after the DD discharges for tritium removal, H-dominated re-deposited layers were added on D-dominated re-deposited layers. In addition D retained in near surface layers were replaced by H both for re-deposited and eroded area. Accordingly deuterium concentration peaked at a little inside behind the H dominated surface layers for all tiles. The temperature increase during the discharge very likely causes the saturation of hydrogen retention even in the re-deposited layers. Accordingly the global wall saturation was observed in JT-60U. [Copyright &y& Elsevier]

Abstract: The chemical behavior of energetic deuterium implanted into tungsten carbide (WC) samples has been investigated by XPS and TDS. The TDS experiments showed that almost of all deuterium retained in WC was desorbed in the temperature region from 300 to 700K and the residue at around 1000K. The deuterium (D2) desorption peak at around 1000K was found to originate from the desorption of deuterium atom (D) trapped by carbon (C). Its retention was considerably small and was saturated at low deuterium ion (D2 +) fluence. The area of the large D2 desorption peaks, which corresponds to the D retention in WC, increased as D2 + fluence increased. The D2 desorption in the temperature range of 300–700K takes place in three stages, the lower two peaks were attributed to the desorption of D retained in two interstitial sites, and the highest peak corresponds to D trapped by carbon vacancies induced by chemical sputtering of C by energetic D2 +. From these experimental results, the D trapping and detrapping behaviors are discussed and it is concluded that the hydrogen isotope retention is governed by the amount of interstitial sites and carbon vacancies in WC. The hydrogen isotope retention could be lowered if the surface temperature of WC were above 700K. [Copyright &y& Elsevier]

Abstract: Retention profiles of hydrogen and deuterium in graphite tiles placed in the inner divertor region of JT-60U were analyzed by secondary ion mass spectroscopy (SIMS) and thermal desorption spectroscopy (TDS). The difference in hydrogen and deuterium retention behaviour is discussed considering the frequency of the strike-point hit and history of NBI heating power. It was found that most of hydrogen/deuterium was retained in the deposited layers, HH deposition layers/DD deposition layers or co-deposited with carbon. Owing to the higher heating power of DD discharges, the deuterium concentration in the DD deposition layers was much lower than that of hydrogen in the HH deposition layers. On the area showing no deposition, very shallow profile of deuterium dominated hydrogen profile. These results indicate that the tritium retention is strongly influenced by the history of discharge and temperatures. Tritium retention on graphite tiles and deposition layers could be significantly reduced with increasing the operation temperature. [Copyright &y& Elsevier]

Abstract: In the present study, the thermal desorption behavior of deuterium implanted into diamond was investigated by means of TDS and XPS. From the results of TDS experiments, the most of all implanted deuterium was desorbed by forming D2 mainly, and two desorption peaks were observed in the temperature range from 700 to 1100K and from 1100 to 1300K. The lower temperature deuterium desorption from the diamond was similar to that from HOPG. However, the D/C value of the diamond was approximately 0.2, which was almost half the value of the HOPG. The C1s XPS spectra of diamond were shifted towards lower energy with increasing heating temperature above 773K. In addition, the π–π∗ transition peak appeared above this temperature. These meant that the disordered diamond structure were reconstructed through the desorption of deuterium, and stabilized by formation of a graphite network. [Copyright &y& Elsevier]