Masahiro Nemoto

Fabrication and Piezoelectric Properties of Grain-Oriented (Bi1/2K1/2)TiO3–BaTiO3 Ceramics

The piezoelectric properties of (1 - x)(Bi1/2K1/2)TiO3–xBaTiO3 (x = 0.1) [abbreviated as BKT–BT10] ceramics prepared by ordinary solid-state reaction and reactive templated grain growth (RTGG) using platelike Bi4Ti3O12 particles as a template were investigated. All samples showed a single-phase perovskite structure, and relative densities compared with theoretical densities were all higher than 95%. The degree of orientation F was determined by the Lotgering method using an X-ray diffraction (XRD) pattern. The F values of textured BKT–BT10 ceramics were relatively low at ~35%. However, field-induced strains and piezoelectric properties of BKT–BT10 ceramics were improved by grain orientation. In particular, the piezoelectric strain constant d33 and the strain of textured BKT–BT10 ceramics in a direction parallel (∥) to the tape stacking direction were 84.5 pC/N and 168 pm/V (at 80 kV/cm), respectively.

Absolute Detection Efficiency of a Microchannel-Plate Detector for Ions and Neutrals

The absolute efficiencies of a microchannel-plate detector for He+ and He0 were measured in the energy range of 1 to 10 keV. There was no difference between He+ and He0 incidences regarding efficiency, and the efficiency was constant in the above energy range. This value indicates that almost all the particles hitting the entrance wall of the MCP pores were detected.

Electrical Properties of Textured (Bi1/2K1/2)TiO3?BaTiO3 Lead-Free Piezoelectric Ceramics

The electrical properties of (1-x)(Bi1/2K1/2)TiO3–xBaTiO3 (BKT–BT100x) ceramics prepared by an ordinary solid-state reaction and a reactive templated grain growth (RTGG) method using platelike Bi4Ti3O12 particles as a template were investigated. The degree of orientation, F, which was determined by the Lotgering method using an X-ray diffraction pattern, achieved ≈83% in the textured BKT–BT10 ceramic. A textured BKT–BT10 ceramic with a homogeneous microstructure was obtained after a long sintering time. The field-induced strains and piezoelectric properties of the BKT–BT10 ceramic were improved by improving grain orientation. In particular, the piezoelectric strain constant, d33, and the normalized strain, d33*, of the textured BKT–BT10 ceramic in the direction parallel (∥) to the tape stacking direction were 121 pC/N and 211 pm/V (at 80 kV/cm), respectively.

Piezoelectric properties of (Bi 1/2 K 1/2 )TiO 3 - BaTiO 3 ceramics with wide working temperatures

Solid solution system, (1-x)(Bi_1/2K_1/2)TiO₃ - xBaTiO₃ (BKT-BT100x), were investigated for evaluating their characterizations and electrical properties as lead free piezoelectric ceramics with wide working temperatures. The BKT-BT100x ceramics of x=0~0.4 indicated high depolarization temperature, T_d, around 300°C. Piezoelectric properties such as electro-mechanical coupling factor, k₃₃, and piezoelectric strain constant, d₃₃, for BKT-BT10 are 0.35 and 73.4 pC/N, respectively. From these results, BKT-BT system is the superior candidate of lead-free piezoelectric materials for high power and/or high temperature applications.

Light-Ion Beam Focusing by z-Discharged Plasma Channel

Experimental and theoretical studies of proton-beam focusing by a z-discharged plasma channel that produces an azimuthal magnetic field are presented. The channel is produced in a Pyrex tube (50 mm in diameter, 140 mm in length) at a pressure of 0.2 Torr (air), which is fired by a fast capacitor bank (1.9 µF, 60 kV). A proton beam extracted from a flat-type, magnetically-insulated diode (850~990 kV, 80 kA, 75 ns) is injected into the channel which is typically fired at voltage ~32 kV and current ~52 kA. Experimentally, we have observed the density enhancement at the focal point with a factor of (11~15). Numerical calculation has also been carried out on trajectories of proton beams, assuming them only to be subject to Lorentz force. A reasonable agreement between the experiment and the theory is obtained on the focusing point or the enhancement factor of the density.

Control of Microstructures of Textured (Bi1/2K1/2)TiO3-BaTiO3 Ceramics

Control of the microstructures of (1–x)(Bi1/2K1/2)TiO3-xBaTiO3 (x = 0.1) [abbreviated as BKT–BT10] ceramics prepared by a reactive templated grain growth (RTGG) using platelike Bi4Ti3O12 particles as a template were investigated. All samples showed a single-phase perovskite structure. The degree of orientation F, which was determined by the Lotgering method using X-ray diffraction pattern, achieved only ∼ 60% in textured BKT-BT10 ceramics. Textured BKT-BT10 ceramics with a homogeneous microstructure were obtained by the the longer sintering time. It is very important to perform long sintering in order to promote the grain growth and improve the orientation factor for this composition.

A Parasitic Effect in Neutral Particle Diagnostic Using a Helium Probing Beam

This paper describes the characteristic and the physical picture of a parasitic disturbance, which can occur because of the drift motion of probing beam ions trapped at the plasma edge, in active neutral particle measurements for magnetically confined fusion devices. In the JT-60 experiments, the disturbance is observed under the condition in which a neutral particle analyzer views the high recycling region, i.e., the divertor, and the occurrence of the parasitic effect is substantially dependent on the safety factor at the plasma boundary. Also discussed are the validity of our interpretation and some measures for avoiding the disturbance.

Proton-beam propagation through Wall-confined plasma channel stabilized against Sausage instability

Experimental results are presented of proton-beam (energy ~650 keV) propagation through wall-confined plasma channel that is stabilized against sausage instability by an externally-applied longitudinal magnetic field. Significant improvement of beam-propagation efficiency has been obtained of ~70% compared with the previous experiment of ~55% without the magnetic field. The propagation can also be available up to ~30% even in a non-propagation region in a non-stabilized channel.