Yoshio Kawate

Formation of cubic boron nitride films by arc‐like plasma‐enhanced ion plating method

Thin cubic boron nitride (cBN) films were synthesized at 350 °C on various substrates such as silicon, stainless steel, TiN‐coated WC–Co and WC–Co by means of an arc‐like plasma‐enhanced ion plating process. In this process, polycrystalline cBN films were obtained at deposition rates of 0.004 to 0.03 μm/min. The infrared spectra showed strong absorption at 1050 cm−1, indicating cubic structure of the deposited film. The electron diffraction patterns also showed the cubic structure, with a lattice parameter of 3.63 A. It is inferred that ion bombardment during film growth plays a important role in the formation of cBN films. The cBN films deposited in this process had a high compressive stress of 4×1010dyn/cm2, which is significantly greater than the value of hard amorphous boron nitride (iBN) films, 1.6×1010dyn/cm2. The internal stress of cBN films was greatly reduced if iBN was used as a buffer layer between cBN and substrate.

Operation of a 920-MHz high-resolution NMR magnet at TML

A 920-MHz high-resolution NMR spectrometer has been operating at the Tsukuba Magnet Laboratory (TML) since April 2002. It has proved its effectiveness by determining the 3-D structures of protein molecules. To accelerate studies in structural biology and solid-state NMR, a second high-field NMR magnet was developed and installed at TML. Although its basic design was the same as that of the first magnet, some improvements were made. For the innermost coil, a 16%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor was employed. The increase in the critical current density above that of a 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor made it possible to reduce the conductor size from 3.5 mm /spl times/ 1.75 mm in the first magnet to 2.80 mm /spl times/ 1.83 mm in the second. At the same operating current of the first magnet, the second magnet is expected to operate at 930 MHz. The liquid helium reservoir and the superfluid helium cooler, which were separated in the first system, were united in the same chamber in the new magnet. The latter magnet was energized up to 21.9 T without quenching in March 2004 and has operated in a persistent-mode at that field. It will be utilized mainly for solid-state NMR measurements.

Optimization of single crystal preparation of Bi2Sr2CaCu2Ox superconductor by the travelling solvent floating zone method

Optimization of single crystal preparation of the Bi2.2(Sr, Ca)2.8Cu2.0Oy superconductor by the travelling solvent floating zone method has been performed with the intention of obtaining large single crystals and improving the superconductive transition temperature, Tc. The composition ratio, Sr/Ca, and the oxygen partial pressure of growth atmosphere, PO2 , were varied in the crystal growth. A single crystal typically obtained was a thin plate of the dimensions of 5×50×2 mm3. The thickness of the crystal was the largest in the crystal growth at Sr/Ca=1.4, while no distinct change was observed in the resulting crystals in the range of 22~100 kPa. Electric and magnetic properties, the formal charge of copper ions and existence of ion defects are discussed.

Development of 1 GHz superconducting NMR magnet at TML/NRIM

Development of a 1 GHz superconducting NMR magnet is in progress at the Tsukuba Magnet Laboratory of the National Research Institute for Metals. The magnet will consist of two parts. The outer magnet of LTS coils is designed to generate a field of 21.1 T (900 MHz) in persistent current mode. The inner coil is designed to generate an additional 2.4 T, resulting in a central field of 23.5 T (1 GHz) in a 54 mm diameter bore at room temperature. As a high-resolution NMR magnet, field stability as well as field homogeneity is very important, which is especially difficult to achieve in the inner coil when exposed to extremely high magnetic fields that superconducting magnets have not yet encountered. The engineering design is complete and fabrication of the superconductors has begun. This report presents the results of the engineering design and R&D studies on the candidate superconductors for the inner coil, such as BSCCO, and improved Nb/sub 3/Al and Nb/sub 3/Sn.

Persistent-mode operation of a 920 MHz high-resolution NMR magnet

Development of a high-field NMR magnet has been underway at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. The magnet succeeded in a persistent-mode operation at 21.17 T in December 1999. A 283-day long-term operation was carried out from October 2000 to August 2001. It included a persistent operation at 21.6 T (920 MHz) for 108 days. This was the highest field that the superconducting magnets have ever achieved in a persistent operation. Field decay was less than 2 Hz/h. Field homogeneity after correcting with superconducting shim coils were less than 0.1 ppm in a sample volume. These results confirmed that this magnet had been successfully developed as a high-resolution NMR magnet.

Development and operation of superconducting NMR magnet beyond 900 MHz

As a milestone in the 1-GHz NMR magnet project being carried out at the Tsukuba Magnet Laboratory, a 900-MHz class NMR magnet was successfully manufactured and operated in December 1999. The developed magnet is made of 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn, Ta-reinforced (Nb,Ti)/sub 3/Sn, and NbTi conductors. The room temperature bore of the cryostat is 54 mm is diameter. All the coils are cooled with pressurized superfluid helium. The magnet generated a field of 21.20 T in a driven mode and then operated in a persistent mode at 21.17 T corresponding to a proton NMR frequency of 902 MHz. The field may be raised to the range of 21.6 T (920 MHz) in the near future.

Layer-by-layer epitaxial growth of a Bi2Sr2CuO6 thin film on a Bi2Sr2CaCu2O8 single crystal

The epitaxial growth of a Bi2Sr2CuO6 (2201) thin film on a Bi2Sr2CaCu2O8 (2212) single crystal has been performed using computer‐controlled laser molecular beam epitaxy. The surface of the 2212 single crystal used as the substrate is smooth and invariant under the growth condition at 640 °C in NO2 pressure of 1×10−5 mbar. The growth process of the 2201 film has been observed by in situ reflection high‐energy electron diffraction (RHEED), and the layer‐by‐layer growth of the 2201 phase is confirmed by the oscillation of RHEED intensities. During the growth, a modulated surface structure which is characteristic of the Bi cuprate crystals is always present.

Application of magnetic resonance imaging to non-destructive void detection in watermelon

A novel application of magnetic resonance imaging (MRI) is described. The possibility of utilizing MRI for non-destructive quality evaluation of watermelons was studied. In this study, we applied MRI to the detection of internal voids in watermelons. In order to increase the measurement rate, we employed a one-dimensional projection profile method instead of observing a two-dimensional cross-sectional image. The void detection was carried out with this technique over 30 samples and 28 samples were correctly evaluated. The measurement rate was 900 ms per sample, which is an acceptable speed for a sorting machine in the agricultural field.

Development and testing of superfluid-cooled 900 MHz NMR magnet☆

Abstract As the preliminary step for the 1 GHz NMR spectrometer, a 900 MHz class NMR magnet was fabricated and was successfully operated in December 1999. The magnet is made of 15% Sn–bronze-processed (Nb,Ti) 3 Sn, Ta-reinforced (Nb,Ti) 3 Sn, and NbTi conductors. All the coils are cooled with pressurized superfluid helium. The magnet generated a field of 21.20 T in a driven mode and then operated in a persistent mode at 21.17 T corresponding to a proton NMR frequency of 901.2 MHz. During the magnet excitation for 24 h, the superfluid bath temperature was kept constant to below 1.6 K using an automatic control system. After several excitation tests, the magnet was quenched and the rupture disk of the magnet vessel was broken. The size of the cold safety valve and the structure of the rupture disk have been checked and modified. Before the reassembly of the magnet cryostat, the modified superfluid cooler for cooling the magnet bath was tested.

Fabrication of superconducting joints for Bi-2212 pancake coils

To evaluate the possibility of persistent current operation for NMR/MRI using a Bi/sub 2/Sr/sub 2/CaCuO/sub 8/ (Bi-2212) superconductor at 4.2 K, the temperature dependence of magnetic relaxation of the single crystal has been measured. It was found that the operating current must be one-fourth of J/sub c/ at 4.2 K to satisfy the stability condition for NMR/MRI operation ( Delta J/J less than 0.005 ppm/h). A superconducting coil made of Bi-2212 silver-sheathed wire was fabricated by the partial melt growth process. The authors were successful in generating 1.60 T in a zero external magnetic field at 4.2 K with a coil made of silver-sheathed Bi-2212 tape which was 100- mu m thick, 10-mm wide and 150-m long. Superconducting jointed pancake coils with critical current reaching 80 A in an external magnetic field of 1.0 T at 4.2 K were also fabricated.<<ETX>>