Masao Hashiba

A quantitative analysis of surface segregation and in-depth profile of copper-nickel alloys

Abstract By utilizing the difference in escape length of the Auger electrons with different energies, a calculation of the in-depth distribution of atomic concentration at the surface is presented on the basis of Palmbergs physical mechanism. Experimental results on clean surfaces of Cu-Ni alloys over the entire composition region with Auger spectroscopy were performed to make the in-depth profile of surface composition caused by annealing. The alloy composition of the first atomic layer at the surface was plotted against the bulk composition, showing significant enric enrichment of Cu atoms in that layer. The results indicated that the segregation takes place in about four atomic layers at the surface.

Gas permeability of SiC/SiC composites as fusion reactor material

Permeability of helium gas in SiC/SiC composites material, which is one of the most important properties in application of SiC/SiC composite for first wall and blanket of fusion reactors, was studied by using a vacuum apparatus. Three tubular and two flat plate SiC/SiC composites were prepared by different preparation processes. The measurement of permeability coefficient of helium gas was carried out with pressure ranging from 10 2 to 10 5 Pa at room temperature. The permeability coefficient of the SiC/SiC composite largely depended on the preparation method. In three tubular materials, the SiC/SiC composite made by both polymer impregnation and pyrolysis (PIP) and melt infiltration (MI) methods showed the lowest permeability, 9.1 x 10 -7 m 2 /s, which was approximately two orders of magnitude smaller than one of the material made only by PIP method. The permeability of the flat plate SiC/SiC composites made by both liquid phase sintering (LPS) and hot pressing (HP) was approximately 1.5 x 10 -9 -4.0 x 10 -11 m 2 /s. The difference of permeability was related to the microscopic structure, i.e. pores and cracks.

Oxide layers on GaAs prepared by thermal, anodic and plasma oxidation: In-depth profiles and annealing effects

Abstract The in-depth profiles of oxide layers prepared by thermal, anodic or plasma oxidation were investigated by means of simultaneous Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) measurements. With the AES measurements it was found that the oxides grown by thermal oxidation consisted only of Ga2O3; a large pile-up of arsenic was found near the interface between the oxide layer and the substrate. In contrast, oxides formed by anodic and plasma oxidation contained both Ga2O3 and As2O3 and showed a much smaller pile-up of arsenic. The annealing of as-grown oxide layers at relatively low temperatures (around 300°C) caused the oxide composition to become more uniform with depth and made the interface thinner. Annealing at relatively higher temperatures gave rise to a deficiency of arsenic in the oxide and created a pile-up of arsenic near the interface. Preliminary X-ray photoelectron spectroscopy measurements revealed the presence of unoxidized arsenic in the sputterer surfaces of anodic and plasma oxides. The SIMS measurements revealed that the relative intensity of the secondary ions varied in a complicated way in the oxide and near the interface, where no appreciable changes in composition were observed by AES. The SIMS results suggest the existence of different oxides having different physiochemical properties; these differences probably alter the ionization yield and/or the process of emission of the secondary ions.

Analysis of the plasma-wall interaction in the Heliotron E device

The plasma-wall interaction (PWI) of the currentless plasmas with temperature To, Tio ≤ 1.1 keV, density Ne = (2–10)× 1013/cm3, and volume-averaged beta value of β

Boronization study for application to large helical device

≤ 2% was investigated. We have observed that PWI took place mainly where the divertor field line intersected the chamber wall (called divertor traces). Boundary plasmas were measured with electrostatic probes, which showed the presence of the divertor region with the parameters in the range of Ned = 1010–1011/cm3 and Ted = 10–50 eV. Surface analysis techniques (ESCA, AES, and RBS) were applied to analyze the surface probes (Si, graphite and stainless steel) and the test pieces (SiC, TiC, and stainless steel), which were irradiated by plasmas for short and long times respectively.

Conditionings for plasma facing walls of large helical device

An experimental device named SUT (SUrface modification Teststand) was constructed for a boronization study. An ultra high vacuum (UHV) condition, a changeable high temperature liner and in situ AES are three distinctive feature of the SUT device. Saturation density of oxygen atoms was as large as 1.2 × 10 17 /cm 2 on a boronized surface, whereas 1.5 × 10 16 /cm 2 on a bare stainless steel surface. It is found by AES analysis that the oxygen-contained layer was as thick as 50 nm from the top surface of the boron film. From such a large oxygen-saturation density, we expect that the oxygen-gettering ability of the boronized surface is likely to be maintained during one-day experiment of LHD. The oxygen-saturation behavior was quite similar between the boronized surfaces obtained with decaborane and diborane, which indicates that, as a working gas of the boronization, the decaborane works well compared with diborane, as far as oxygen gettering is concerned

Probe measurements for impurity transport in the scrape-off layer of JIPP T-II

The first and second experimental campaigns in large helical device (LHD) were carried out from March to December 1998. Before the each campaign, the material probes were placed at the inner wall of vacuum vessel along the poloidal direction. After each campaign, change of surface morphology, impurity depth profile and gas desorption of the samples were examined. In the first experimental campaign, the ECR discharge cleanings were employed. After the first experimental campaign, the surface was modified by the deposition of sub-micron particles, and the concentrations such as oxygen and carbon were still high. Impurity gas desorption was also large in the sample at the port. In the second experimental campaign, the glow discharge cleanings were employed and the number of main discharge shots increased. After the second experimental campaign, no significant deposition took place except for the position close to the divertor leg, and the oxygen impurity level was reduced. In every sample, the helium was retained by the helium glow discharge. In addition, the amount of gas desorption was considerably reduced even in the sample at the port. In the second experimental campaign, the wall conditionings largely progressed by using the glow discharge cleanings and the increase of main discharge shots with a high heating power.

Measurements of oxidation velocities for graphites, silicon and boron mixed graphites.

Impurity transport processes in the scrape-off layer of the JIPP T-II device have been studied by a probe method. A cubical silicon probe was inserted and exposed to 20 identical tokamak discharges in the scrape-off region. Deposited impurities were analysed with use of AES, RBS and PIXE equipments. The main metallic impurities were molybdenum and iron whose deposition behavior was almost the same on any side of the probe, and their fluxes were observed to be 1.2 × 1013/cm2· discharge on the electron drift side and 5.2 × 1013/cm2· discharge on the ion drift side, respectively at the distance of 18.3 cm from the center line of the plasma. The mean transport energy of the impurities striking the probe surface was estimated from the depth concentration profile applying the LSS theory for iron as 90 eV on the electron drift side and 250 eV on the ion drift side, respectively. The e-folding length of the scrape-off plasma density was measured by the radial distribution of a deposited tantalum amount to be 0.64 cm on the electron drift side and 1.73 cm on the ion drift side, respectively.

Study on in-situ carbon coating in JIPP T-IIU

Oxidation velocities of isotropic graphite, pyrolytic carbon, silicon and boron mixed graphites were measured by using a vacuum microbalance of Cahn RG type under an oxygen pressure of 1.33 kPa and temperature range of 650~900°C. For isotropic graphites with different ash concentrations, it was observed that the oxidation velocity increased as the ash concentration when the temperature was below 750°C. The pyrolytic carbon had the oxidation velocity approximately an order of magnitude smaller than that of the isotropic graphite. The oxidation velocity of silicon mixed graphite linearly decreased as the increase of silicon concentration. In a case of boron mixed graphite, the oxidation was considerably suppressed by the boron content and the weight gain was observed due to the formation of B2O3 when the boron concentration exceeded approximately 10%.

Surface study of Type 6063 aluminium alloys for vacuum chamber materials

The effectiveness of the in-situ carbon coating (carbonization) has been demonstrated to reduce the radiation loss by iron impurities during ICRF heating in the JIPP T-IIU tokamak. As a result of carbonization, the total radiation loss decreased down to one fifth of the RF power, which resulted in an increase in electrons and total stored energy compared with these conditions before carbonization. The thickness of the carbon layer was 300–900 A, and its toroidal uniformity was within a factor of 3, although only one anode and one gas-inlet were used. A thin carbide layer is formed between the C-film and the stainless steel substrate with carbonization at room temperature. The hydrogen concentration is 40–50 at.% in the carbon layer. Deposition of carbon was observed on window materials. The deposition rate was relatively less on electrical insulators compared to the deposition rate on metals.