[en] Brief item

[en] Published in summary form only

[en] Arc erosion measurements of the materials for limiters and first walls in fusion devices are of importance in the fusion technology so as to help in estimation of plasma contamination. In this brief report, erosion rates due to arcing were measured for 316 stainless steel, titanium, titanium nitride coated on graphite, and titanium carbides coated on 440C stainless steel and graphite. The characteristic features of the experiment for a simulation study of arc erosion in fusion devices were on the points that test materials were irradiated before arcing with deuterium ions, helium ions and heavy (''self'')-ions, and that the irradiated materials were arced in hydrogen plasma produced beforehand. The erosion was observed by a SEM and a surface roughness gage. The mass loss of materials was measured by a microbalance. As the effects of pre-irradiation, the results show that arcs were inductive at the irradiated region, and that the erosion rates were enhanced by irradiation

[en] We examined a concentration of Bi defects in layered Bi Ch ₂ based superconductors Ln O_1-xF_xBi Ch ₂ ( Ln = La, Ce, Nd Ch = S, Se). These materials show superconductivity by electron carrier doping into Bi Ch ₂ layer. Since Bi defects affect the carrier concentration directly, an examination of the concentration is important to evaluate an actual carrier concentration. In this paper, the concentration of Bi defects on the Bi Ch ₂ layers in Bi Ch ₂ based superconductors was evaluated by scanning tunneling microscopy measurements in real space. We found the samples with BiSe₂ layers have less Bi defects than those with BiS₂ layers. Furthermore, the concentration of Bi defects was found to be almost constant regardless of F concentration and Ln ion. (paper)

[en] 1 T -TaS₂ has been known to undergo Mott transition from nearly commensurate charge density wave (CDW) state to commensurate CDW state at about 200 K. Recently, Fe doping was found to suppress the Mott transition and induce superconductivity. In this study, we report on the scanning tunneling microscopy (STM) and spectroscopy (STS) study on Fe doped 1 T -TaS₂ with different Fe concentration. STM observations reveal that the CDW superlattice becomes irregular as increasing Fe concentration. STS measurements uncover the spatial change in the local density of state (LDOS). We find two types of David-star: one has symmetric LDOS with respect to Fermi energy, and the other has asymmetric one. We identify that the asymmetric spectrum is due to an Fe dopant. (paper)

[en] We report on a systematic scanning tunneling microscopy and spectroscopy (STM/STS) study on 1T–TaS_2-xSe_x (x = 0, 0.3, 1.0) at 4.2 K. While the compounds with x = 0 and 0.3, which undergoes the Mott transition, showed the commensurate charge density wave (CDW) with the period of $\sqrt{13}{a}_0\times <!--\; ??\; -->\sqrt{13}{a}_0$ (a ₀ is in-plane lattice constant), the compound with x=1, which shows superconductivity at 3.5 K, exhibits anomalous domain structure: The domain structure consists of regions with regular array of David-stars divided by bright contrasted walls at positive bias voltage. We found the domain wall showed the different electronic state from that of the domain. (paper)

[en] This paper describes the applicability of the numerical method and forward speed effect for hydrodynamic forces and motions on large offshore structures with a constant forward speed in waves. The authors developed the computer program to calculate the hydrodynamic forces and motions on three-dimensional bodys using the three-dimensional source distribution method with a constant forward speed. As for a cone type platform model with a constant forward speed, wave exciting forces, added mass and damping coefficients and motions were calculated by this numerical method and compared with the experimental values of forward speed Fn = 0.0, 0.055 and 0.11, respectively. The calculated results and the experimental results are shown a good correlation within the linear theory

[en] We present scanning tunneling microscopy and spectroscopy measurements on a cleaved surface of the LaO_0.9F_0.1BiSe₂ single crystals. Tunneling spectra show a finite local density of states at E _F, which is consistent with metallic conductivity in bulk. In addition, the existence of the supermodulation running along the diagonal directions of Bi square lattice was revealed. The period of the supermodulation was about 3 to 5 times the length of the lattice constant. This period is close to that observed in LaO_0.5F_0.5BiSe₂. (paper)

[en] Transition metal dichalcogenides 2H-TaS₂ and 2H-TaSe₂ show charge density wave (CDW) state and superconductivity. It has been reported that elemental substitution of chalcogenide suppresses the CDW and enhances superconductivity. However, how the CDW order is suppressed by the substitution has not been clarified yet. To clarify this, we performed real space observation of the CDW state in the commensurate phase of 2H-TaS_1.8Se_0.2 by scanning tunneling microscopy. The existence of domains separated by walls at which the phase of the CDW shifts was observed. The change in the electronic state on the domain boundaries in 2H-TaS_1.8Se_0.2 was not as drastic as that in 1T-Fe_xTa_1-xS₂. (paper)

[en] We have developed 100-pixel Nb/Al based superconducting tunnel junction (STJ) array detectors which was enlarged the pixel size to improve X-rays detection throughput. The two different sizes of 100 μm × 100 μm and 160 μm × 160 μm STJs which consisting of Nb (100 nm)/Al (70 nm)- AlO_X/Al (70 nm)/Nb (300 nm) were fabricated to determine the effective size of a single STJ. The leakage current, the fabrication yield and the energy resolution for Al- K _α of 100 μm-square and 160 μm-square STJs were 9.3 ± 4.6 nA and 12.3 ± 9.7 nA, 85 % and 84 %, 23.6 ± 4.6 eV and 27.5 ± 3.8 eV, respectively. Since these exhibited almost equal performance, it is found that STJs with a size of 160 μm × 160 μm can be used as a high throughput X-ray detector. (paper)