Kenji Yamauchi

A New Technique for the Formation of Ultrafine Particles by Sputtering

A gas evaporation technique using sputtering is newly developed. The characteristic of this new technique is the use of sputtering in an atmosphere of higher gas pressure such as 0.5 to 100 Torr than is used for ordinary sputtering. W, Ag and Cu are tested and their ultrafine particles are formed. WC1-x particles are also prepared by reactive sputtering.

Attempt to form hydride and amorphous particles, and introduction of a new evaporation method

Al and TiH2 particles of fcc structure can be produced in an atmosphere of gaseous H2 at reduced pressure. Al particles with definite habit are obtained, which has been never observed in the ordinary gas evaporation technique using a HV system. The habit of TiH2 particles grown in the intermediate zone of the smoke is determined to be a dodecahedron. The growth is considered as the result of the martensite transformation from the bcc structure initially formed to the fcc structure accompanying a slight modification of the characteristic habit as observed for Ti particles. For the preparation of amorphous particles, first, the quenching rate of a particle, dTdt was estimated to be more than 104°Cs. Ultrafine particles of Pd80Si20 chosen as a test sample did not show the amorphous structure, but the crystalline. Application of the sputtering method as a new evaporation source in the gas evaporation technique is attempted. With the sputtering method, W particles with definite habits are produced.

Plasma confinement studies in LHD

The initial experiments on the Large Helical Device (LHD) have extended confinement studies on currentless plasmas to a large scale (R = 3.9 m, a = 0.6 m). Heating by NBI of 3 MW produced plasmas with a fusion triple product of 8 × 1018m-3keVs at a magnetic field strength of 1.5 T. An electron temperature of 1.5 keV and an ion temperature of 1.1 keV were achieved simultaneously at a line averaged electron density of 1.5 × 1019 m-3. The maximum stored energy reached 0.22 MJ with neither unexpected confinement deterioration nor visible MHD instabilities, which corresponds to β = 0.7%. Energy confinement times reached a maximum of 0.17 s. A favourable dependence of energy confinement time on density remains in the present power density (~40 kW/m3) and electron density (3 × 1019 m-3) regimes, unlike the L mode in tokamaks. Although power degradation and significant density dependence are similar to the conditions on existing medium sized helical devices, the absolute value is enhanced by up to about 50% from the International Stellarator Scaling 95. Temperatures of both electrons and ions as high as 200 eV were observed at the outermost flux surface, which indicates a qualitative jump in performance compared with that of helical devices to date. Spontaneously generated toroidal currents indicate agreement with the physical picture of neoclassical bootstrap currents. Change of magnetic configuration due to the finite β effect was well described by 3-D MHD equilibrium analysis. A density pump-out phenomenon was observed in hydrogen discharges, which was mitigated in helium discharges with high recycling.

Attempt to form ultrafine particles with hydride and amorphous structure

TiH2 particles with fcc structure can be produced in an atmosphere of reduced pressure of H2, instead of an ordinary inactive gas, by the gas evaporation technique. The habit of the particles grown in the intermediate zone of a smoke is determined by means of electron microscope to be dodecahedral and consists of 8 {111} and 4 {100}. As in the case of Ti particles, the growth mechanism can be considered as follows: The bcc TiH2 particles initially formed, the high temperature phase, are transformed into fcc structure, the low temperature phase, through the martensite transformation with a slight change of the habit, from the rhombic dodecahedral to simple dodecahedral. For the preparation of amorphous particles, first the quenching rate of a particle, dT/dt was estimated to be more than 104°C/s. The quenching rate was estimated from measurements of the temperature gradient around the evaporation source, dT/dx and the rising velocity of the particles along the convection flow of residual gas, dx/dt. The preparation of ultrafine particles of Pd80Si20 chosen as a test material was attempted. However, the particles showed crystalline rather than amorphous structure.

Magnesium Twinned Particles Grown in Inert Gases

Twinned particles of magnesium prepared using the gas evaporation technique were studied using electron microscopy. Particles with (10.1), (10.3), (11.1) and (11.2) twin planes were found in the smoke outer zone. Their external faces were the same as those of single crystal particles, i.e. {10.0} and (00.1). The growth of the (10.1) twinned particle was more pronounced than that of the other three kinds of twinned particles and from this it was deduced that the twin formation occurs at the nucleation stage.

Growth of fine particles of the Fe-N system prepared by reactive gas evaporation technique

Abstract Evaporation of iron at a reduced pressure varying from a few to 200 Torr of ammonia causes the growth of several kinds of fine particles of the Fe-N system. The particles thus prepared were studied by means of electron microscopy. At a few Torr of gas pressure, particles of α-Fe (bcc) and γ-Fe (fcc) show the truncated rhombic dodecahedron and mainly needle habits, respectively. The former is characteristic of bcc metals while the latter is a modification of the well-known pentagonal decahedron of multiply twinned particles. The lattice parameter of the γ-Fe is 3.64 ± 0.03 A, which corresponds to the nitrogen content of 2.5 wt%. Above 100 Torr of gas pressure, particles of γ′-Fe 4 N grow. The particles collected on carbon films in the inner and outer zones are sometimes aggregated in clusters.

Ultrafine particles produced by Vacuum Evaporation onto a Running Oil Substrate (VEROS) and the modified method

Abstract The growth mechanism of particles produced by the VEROS method is studied through observation of particles formed by vacuum evaporation onto a still oil substrate. The result showed that the mechanism for VEROS does not have a significant difference from that on the still oil substrate. Coalescence growth among particles is inevitable when vacuum distillation is employed to concentrate the particle density in the oil, since the ultrafine particles prepared by VEROS are obtained in the form of suspension in the oil. Replacement of oil with ethyl alcohol enables to avoid the difficulty. A preliminary experiment of vacuum evaporation onto cooled ethyl alcohol was performed.

Construction of a 100-Hz-Repetition-Rate 28-Channel Thomson Scattering System for the JIPPT-IIU Tokamak.

An ASDEX-type Thomson scattering system (YAG Thomson) with an improved performance (100 Hz repetition rate and 1.5 cm spatial resolution) was designed and constructed for the JIPPT-IIU tokamak. Efforts were concentrated on realizing a large solid angle of collection optics (0.08 sr), high throughput of polychromators ( >64%) and high quantum efficiency of detectors (80% at 900 nm), which, together, yield high-quality data even with a small laser energy (0.4 J) delivered by a 100-Hz-repetition-rate Nd:YAG laser and with a short scattering length (1.0 cm). The compactness of the polychromators also contributes to achieving a high spatial resolution.

Simulations and Experiments on O Density and Distribution in Ashing Process Using Surface Plasma Excited by Microwave

Simulation methods for the density and spatial distribution of O atoms have been developed to analyze high-density plasma (1011 cm-3) excited by two microwave sources. The density of O atoms, that react with photoresist, was calculated in a gas mixture of CF4 and O2, and the density has a maximum value at 10% CF4 partial pressure. For the distribution simulation, the rate of reaction between O atoms and photoresist was measured in a small cell, and the sticking coefficient was estimated to be 0.002. The O atom distribution on a glass substrate was calculated by the simulator, where the sticking coefficient was input, focusing on the density under a beam that connected the microwave sources and had no plasma source. The results of both the simulations are in good agreement with the experimental results. The simulations were applied to optimize the chamber configuration and process conditions. As a result, a high ashing rate of over 1430 nm with a uniformity of ±9.3% was obtained.

In Situ Laser Beam Alignment for Thomson Scattering System

An in situ laser beam alignment method was developed for a tokamak plasma Thomson scattering system. The laser beam position was swept rapidly while observing the scattered light signals from 28-channel polychromators, using which the tilt angle and position of the laser beam were optimized.