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Co content (x) dependences of cationic distribution and local fields at the tetrahedral A-site and octahedral B-site nuclei in Co ferrites, CoxFe3−xO4 (x = 0–1.0), were investigated by means of hyperfine interaction techniques. A combined investigation by 57Fe transmission and 57Co emission Mössbauer spectroscopies revealed that about 6% of Co2+ ions occupy the A sites for the sample with Co contents of x = 0 and 1.0. This observation evidently suggests that the site selectivity of Co2+ ions is independent of x for samples prepared on the same heat treatment condition. For hyperfine interaction parameters, obvious x dependence was observed for the B-site Fe nuclei, reflecting variation of the atomic ratio of Fe3+/Fe2+ changing with x, whereas for the A-site Fe nuclei, the parameters hardly change along with x. Contrary to the x-independence for the A-site Fe nuclei, however, it was demonstrated by perturbed angular correlation spectroscopy with the nonmagnetic probe 111Cd(←111In) that the hyperfine field at the A site significantly changes along with x. These contradictory results on the A-site fields verify that the nonmagnetic probe can distinguish a subtle change in the local fields with higher sensitivity. [ABSTRACT FROM AUTHOR]

In this work, we examine how deuterium becomes trapped in plasma-exposed tungsten and forms near-surface platelet-shaped precipitates. How these bubbles nucleate and grow, as well as the amount of deuterium trapped within, is crucial for interpreting the experimental database. Here, we use a combined experimental/theoretical approach to provide further insight into the underlying physics. With the Tritium Plasma Experiment, we exposed a series of ITER-grade tungsten samples to high flux D plasmas (up to 1.5×1022m-2 s-1) at temperatures ranging between 103 and 554 °C. Retention of deuterium trapped in the bulk, assessed through thermal desorption spectrometry, reached a maximum at 230 °C and diminished rapidly thereafter for T>300 °C. Post-mortem examination of the surfaces revealed non-uniform growth of bubbles ranging in diameter between 1 and 10 lm over the surface with a clear correlation with grain boundaries. Electron backscattering diffraction maps over a large area of the surface confirmed this dependence; grains containing bubbles were aligned with a preferred slip vector along the (111) directions. Focused ion beam profiles suggest that these bubbles nucleated as platelets at depths of 200 nm-1 lm beneath the surface and grew as a result of expansion of sub-surface cracks. To estimate the amount of deuterium trapped in these defects relative to other sites within the material, we applied a continuum-scale treatment of hydrogen isotope precipitation. In addition, we propose a straightforward model of near-surface platelet expansion that reproduces bubble sizes consistent with our measurements. For the tungsten microstructure considered here, we find that bubbles would only weakly affect migration of D into the material, perhaps explaining why deep trapping was observed in prior studies with plasma-exposed neutron-irradiated specimens. We foresee no insurmountable issues that would prevent the theoretical framework developed here from being extended to a broader range of systems where precipitation of insoluble gases in ion beam or plasma-exposed metals is of interest. [ABSTRACT FROM AUTHOR]

Exit-angle resolved carbon atom and cluster (C2 and C3) sputtering yields are measured during different noble gas (Xe, Kr, Ar, Ne, and He) ion bombardments from a plasma, for low incident energies (75–225 eV). A quadrupole mass spectrometer (QMS) is used to detect the fraction of sputtered neutrals that is ionized in the plasma and to obtain the angular distribution by changing the angle between the target normal and the QMS aperture. A one-dimensional Monte Carlo code is used to simulate the interaction of the plasma and the sputtered particles in the region between the sample and the QMS. The effective elastic scattering cross sections of C, C2, and C3 with the different bombarding gas neutrals are obtained by varying the distance between the sample and the QMS and by performing a best fit of the simulation results to the experimental results. The total sputtering yield (C+C2+C3) for each bombarding gas is obtained from weight-loss measurements and the sputtering yield for C, C2, and C3 is then calculated from the integration of the measured angular distribution, taking into account the scattering and ionization of the sputtered particles between the sample and the QMS. We observe undercosine angular distributions of the sputtered atoms and clusters for all the studied bombarding gases and a clear decrease of the atom to cluster (C2 and C3) sputtering ratio as the incident ion mass increases, changing from a carbon atom preferential erosion for the lower incident ion masses (He, Ne, and Ar) to a cluster preferential erosion for the higher incident ion masses (Kr and Xe). [ABSTRACT FROM AUTHOR]

We clarified critical factors affecting the crystallographic orientation of LiNbO3 (LN) thin films deposited by electron cyclotron resonance plasma sputtering on transparent conductive oxides, i.e., TiN and indium tin oxide (ITO). When LN films were crystallized during sputtering on amorphous TiN, insufficient crystallization (400 °C), a roughened TiN surface by crystallization (460 and 530 °C), and oxidization of TiN (600 °C) interfered with the production of c-axis oriented textured film. Solid-phase crystallization of amorphous LN film on amorphous TiN through rapid thermal annealing provided a solution to disorientation factors. Because of the low crystallization temperature of ITO, both crystallization during sputtering and solid-phase crystallization by postannealing yielded polycrystalline LN for LN film on amorphous ITO, but with a substantial number of c-axis oriented domains. For both amorphous LN film on polycrystalline TiN and polycrystalline ITO, however, nucleation assisted by seeds at the interface resulted in a completely random orientation. [ABSTRACT FROM AUTHOR]

An investigation was made of the magnetic properties of Nd-Fe-Co-V bulk exchange-spring magnets fabricated by spark plasma sintering and consisting of a hard Nd[sub 2]Fe[sub 14]B phase and a soft α-Fe phase and having a low rare-earth content of Nd = 2-7 at. %. The high saturation magnetization of the bulk exchange-spring magnets was confirmed experimentally, and the measured data agreed well with the saturation magnetization values estimated from their respective rare-earth content. The saturation magnetization values were nearly uniform and were not dependent on changes in the grain size. Additionally, the specific resistance of the samples nearly coincided with the values interpolated from the specific resistances of an ordinary sintered pure Fe bulk compact and a sintered Nd-Fe-B magnet. These results suggest that the α-Fe/Nd[sub 2]Fe[sub 14]B bulk exchange-spring magnets did not contain any appreciable grain boundary phase between the fine nanoscale-size grains or tertiary phase. [ABSTRACT FROM AUTHOR]

A transportable and rugged cylindrical magnetic shield (length 120 cm, inner diameter 36.5 cm, and weight 43 kg) is fabricated by compositing Co-based amorphous magnetic tapes and a toroidally wound copper-wire shaking coil with fiber-reinforced plastics (FRP). The innermost and the outermost part of the cylinder are made of carbon fiber-reinforced plastics (CFRP) for obtaining a rugged structure. The shielding factor evaluated for the transversally applied 10 Hz, 10 μT magnetic field was better than 10 000 at the shaking condition of 400 Hz, 1.9 A/m, which requires only a 0.76 V A shaking source. [ABSTRACT FROM AUTHOR]

The low rare-earth content α-Fe/Nd[SUB2]Fe[SUB14]B nanocomposite magnets having a high soft phase ratio) were fabricated by the rapid quenching method and evaluations were made of the crystallization behavior, microstructure, and magnetic properties in the annealing process. An investigation of the relationship between the roller surface velocity, V[SUBs], and magnetic properties showed that changes)in the crystal grain size of the α-Fe phase following annealing could be attributed to differences in the amorphous content of the as-melt-spun ribbons. As the amorphous content was increased, their crystal grain size tended to become finer and their magnetic properties tended to improve. However, it was observed that the optimum rapid quenching rate exists. The slight presence of clusters in as-melt-spun ribbons is favorable for obtaining good magnetic properties because the growth of a-Fe crystals is inhibited. The presumed reason for this inhibiting effect is that α-Fe growth occurs in a process in which clusters containing Nd expel this element. In the case of a completely amorphous state, large crystals grew easily, because they consisted of only Fe and Co in the initial stage. [ABSTRACT FROM AUTHOR]

Understanding tritium retention and permeation in plasma-facing components is critical for fusion safety and fuel cycle control. Glow discharge optical emission spectroscopy (GD-OES) is shown to be an effective tool to reveal the depth profile of deuterium in tungsten. Results confirm the detection of deuterium. A ~46 μm depth profile revealed that the deuterium content decreased precipitously in the first 7 μm, and detectable amounts were observed to depths in excess of 20 μm. The large probing depth of GD-OES (up to 100s of μm) enables studies not previously accessible to the more conventional techniques for investigating deuterium retention. Of particular applicability is the use of GD-OES to measure the depth profile for experiments where high deuterium concentration in the bulk material is expected: deuterium retention in neutron irradiated materials, and ultra-high deuterium fluences in burning plasma environment. [ABSTRACT FROM AUTHOR]

The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile. [ABSTRACT FROM AUTHOR]

This article describes a diagnostic for measuring neutron emission profile in JT-60U. The Stilbene neutron detector, developed by TRINITI laboratory in Russia, has been installed on the JT-60U Tokamak to measure the neutron emission profile for the first time. The Stilbene neutron detector is a detector which combines a Stilbene crystal scintillator with a neutron-gamma pulse shape discrimination circuit, with a very compact size. Performance tests were carried out using neutron and gamma-ray source prior to installation on JT-60U. Good gamma suppression of the Stilbene neutron detector was verified. Though the neutron emission profile obtained by Stilbene neutron detectors has error of 30% in innermost channel with a calculation using measured plasma parameters, there is an agreement within 10% error in the other channels. [ABSTRACT FROM AUTHOR]

Reports on the construction of low-Reynolds-number type models with the aid of direct numerical simulations databases. Incorporation of velocity and time scales to represent various sizes of eddies in velocity and thermal fields; Validity of the model; Governing equations for velocity and thermal fields.

A high-current ECR source has been developed for oxygen implanters for use in fabricating separation by implanted oxygen (SIMOX) substrates. The new source has the following features: (1) high-current density (150 mA/cm²) and large extracted current (more than 200 mA), (2) stable and long lifetime operation (more than 200 h), (3) high O[sup +] ratio (more than 80%), and (4) low-divergence beam. The improved performance is obtained by incorporating the following: (1) Localized high-density plasma generation at the center of the plasma chamber. (2) A newly developed multilayer window to satisfy two requirements: efficient coupling of the microwave with high-density plasma and high resistance to high-speed backstream electrons. (3) Optimized combination of plasma chamber length and axial magnetic field distribution. (4) Sophisticated compact magnetic circuit that yields the Optimum magnetic field for obtaining high-density plasma. An industrial-version ECR source was developed for production use on EATON NV-200 implanters. The source was installed on an NV-200 and used to implant oxygen ions to Si wafers. Good performance compared to a duopigatron source was obtained in terms of beam transport efficiency and reliability of source operation. [ABSTRACT FROM AUTHOR]

AlGaAs/GaAs surface-emitting laser diodes (SELDs) with distributed Bragg reflectors (DBRs) and current blocking layers are fabricated with the combination of a two-step epitaxial growth and the reactive ion beam etching (RIBE) technique. An Al0.1Ga0.9As/Al0.7Ga0.3As multilayer and an amorphous silicon (a-Si)/silicon dioxide (SiO2) multilayer are employed for the lower and upper mirrors, respectively. The active region has a 5×5 μm or 4 μm [lowercase_phi_synonym] area and a 0.8 μm thickness. The minimum threshold current is 3.3 mA under pulsed condition and 4.1 mA under continuous wave (cw) operation at 12 °C with junction-side-up configuration. Stable single longitudinal mode is observed, and far-field pattern (FFP) indicates higher transverse mode operation. [ABSTRACT FROM AUTHOR]

A transverse mode stabilized GaAlAs laser diode which includes a ZnSe layer for the waveguide has been developed. The double heterostructure of the GaAlAs laser is formed by low-pressure metalorganic chemical vapor deposition (MOCVD), and a ZnSe layer is grown by adduct-source MOCVD in order to block the injection current and change the real refractive index in the lateral direction. The fundamental transverse mode oscillation of more than 15 mW is obtained with a low threshold current of 28 mA and a high quantum efficiency of 76%. An output power as high as 25 mW is achieved. [ABSTRACT FROM AUTHOR]

Experiments have been conducted on Constance B to study transport properties in electron cyclotron resonance (ECR) heated plasmas of high-charge-state neon ions. Measurements were made of confinement parallel and perpendicular to the magnetic field at heating frequencies of 10.5 and 14 GHz, and corresponding ECR magnetic field strengths. Although radial ion losses scaled approximately as B[sup -2], the total particle confinement time was independent of magnetic field. Thus, higher current densities of multicharged neon ions were extracted at higher ECR heating frequency and magnetic field. [ABSTRACT FROM AUTHOR]

The soft x-ray continuum radiation in tokamak fusion test reactor (TFTR) low-density neutralbeam discharges can be much lower than its theoretical value obtained by assuming a corona equilibrium. This reduced continuum radiation is caused by an ionization equilibrium shift toward lower states, which strongly changes the value of the average recombination coefficient of metallic impurities &&gammamacr;, even for only slight changes in the average charge &&Zmacr;. The primary agent for this shift is the charge exchange between the highly ionized impurity ions and the neutral hydrogen, rather than impurity transport, because the central density of the neutral hydrogen is strongly enhanced at lower plasma densities with intense beam injection, in the extreme case of low-density, high neutral-beam power TFTR operation (energetic ion mode) the reduction in &γmacr; can be as much as one-half to two-thirds. We calculate the parametric dependence of &γmacr; and ¯ for Ti, Cr, Fe, and Ni impurities on neutral density (equivalent to beam power), electron temperature, and electron density. These values are obtained by using either a one-dimensional impurity transport code or a zero-dimensional code with a finite particle confinement time. As an example, we show the variation of &γmacr; and &&Zmacr; in different TFTR discharges. [ABSTRACT FROM AUTHOR]

Metal impurity concentrations are measured by the pulse-height-analyzer (PHA) diagnostic from Kα x-ray peak intensities by use of an averaged excitation rate 〈συ〉. Low-Z impurity concentrations are inferred from the continuum enhancement (relative to a pure plasma) minus the enhancement due to metals. Since the PHA does not resolve lines from different charge states, 〈συ〉 is a weighted sum of rates; coronal equilibrium is usually assumed. The 〈συ〉 used earlier omitted the intercombination and forbidden lines from the dominant heliumlike state. The result was an overestimate of metals and an underestimate of low-Z impurities in cases where metals were significant. Improved values of 〈συ〉 using recent calculations for H-, He-, and Li-like Fe range from 10% to 50% larger than the earlier rates and yield metal concentrations in better agreement with those from vacuum ultraviolet (VUV) spectroscopy. [ABSTRACT FROM AUTHOR]

The mid-infrared range is an important spectrum range where materials exhibit a characteristic response corresponding to their molecular structure. A free-electron laser (FEL) is a promising candidate for a high-power light source with wavelength tunability to investigate the nonlinear response of materials. Although the self-amplification spontaneous emission (SASE) scheme is not usually adopted in the mid-infrared wavelength range, it may have advantages such as layout simplicity, the possibility of producing a single pulse, and scalability to a short-wavelength facility. To demonstrate the operation of a mid-infrared SASE FEL system in an energy recovery linac (ERL) layout, we constructed an SASE FEL setup in cERL, a test facility of the superconducting linac with the ERL configuration. Despite the adverse circumstance of space charge effects due to the given boundary condition of the facility, we successfully established the beam condition at the undulators and observed FEL emission at a wavelength of 20 μm. The results show that the layout of cERL has the potential for serving as a mid-infrared light source.

The tritium plasma experiment (TPE) is a unique facility devoted to experiments on the behavior of deuterium/tritium in toxic (e.g., beryllium) and radioactive materials for fusion plasma-wall interaction studies. A Langmuir probe was added to the system to characterize the plasma conditions in TPE. With this new diagnostic, we found the achievable electron temperature ranged from 5.0 to 10.0 eV, the electron density varied from 5.0 × 10(16) to 2.5 × 10(18) m(-3), and the ion flux density varied between 5.0 × 10(20) to 2.5 × 10(22) m(-2) s(-1) along the centerline of the plasma. A comparison of these plasma parameters with the conditions expected for the plasma facing components (PFCs) in ITER shows that TPE is capable of achieving most (∼800 m(2) of 850 m(2) total PFCs area) of the expected ion flux density and electron density conditions.