Fumiaki Matsumoto

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.

Improved J/sub c/ property of Bi2223 tapes made using AgCu alloy-sheath doped with Ti, Zr, Hf or Au

Bi2223 superconducting tapes have been prepared by the powder-in-tube technique using Ag-10at%Cu-xat%M (x=0-1.0, M=Ti, Zr, Hf or Au) alloy sheaths. The alloy-sheathed tape samples, prepared by repeating 2 or 3 times of sintering and cold pressing, showed high J/sub c/ values. The higher critical current densities, J/sub c/s, 5-6/spl times/10/sup 4/A/cm/sup 2/, at 4.2 K, 14 T were obtained for the Ag-10at%Cu-(0.03-0.1at%Ti, 0.1at%Zr, 0.1at%Hf and 0.3at%Au) tape samples. Microstructural examinations of these samples revealed a modified Bi2223 grain structure at the sheath/core interface and also a denser and more aligned microstructure. X-ray diffraction analysis, vibrating sample magnetometer measurement and ac susceptibility studies seem to suggest an enhancement of the Bi2223 phase formation with high T/sub c/ and improved texture, resulting in higher J/sub c/.<<ETX>>

RETENTION OF IONS IN A MAGNETIC CHROMATOGRAPH USING HIGH-INTENSITY AND HIGH-GRADIENT MAGNETIC FIELDS

The control of the retention and separability of samples to be analyzed with high performance liquid chromatography systems is difficult, and usually requires exchanging of the mobile phase and/or the column. We developed a magnetic chromatography (MC) system, which does not require regular exchanging of the mobile phase and/or the column, and uses a continuous-flow system to separate multiple ionic species with different magnetic properties. To demonstrate experimentally the feasibility of such an MC system, we measured the retention of ions in the MC system for aqueous solutions of either pure NaI, CuSO4, NiCl2, CrCl3, or CoCl2. We applied magnetic fields varying from 0 to 3 T to the aqueous solution of transition element cations and anions flowing in an MC system, and demonstrated that the retention time was delayed by about 20 min, and that for Co(II) the chromatogram broadened with increase in the applied magnetic field intensity (H). Furthermore, our results suggest that for ionized transition elements with a larger Bohr magneton number, the retention time in MC systems becomes longer. We derived experimentally a retention factor, k, that can be simply expressed in terms of an MC parameter, p MCH , which is the product of the Bohr magneton number, the concentration of the cations, and H. The MC parameter can be used to correlate all experimental data in terms of k, as k= 0.0014p MCH 1.47. Hence, k is proportional to about 3/2 power of the MC parameter. We therefore confirmed that there is a significant effect of high-intensity, high-gradient magnetic fields on the behavior of paramagnetic cations in water.

Superconducting inserts in high-field solenoids

The critical currents of the innermost coil mainly limit the highest field of the present superconducting solenoids. For this reason, the insert coils in high-field solenoids are often wound with newly developed superconductors to increase their highest fields. This is a good demonstration of the high-field performance of the newly developed conductors. Design issues of high-field superconducting inserts are overviewed. Representative examples that have been carried out and are now in progress are introduced.

Test results of long term operation of the superfluid-cooled cryostat for a 1 GHz NMR spectrometer

A superfluid cryostat for an 1 GHz-NMR magnet has been developed and its performance was tested. The magnet was successfully energized up to 21.6 T corresponding to a resonance frequency of 920 MHz this April. Before the 920 MHz operations, the magnet was operated for 5 months at the 900 MHz field to check the long-term reliability of the cryogenic system. Stable cryogenic performance has been confirmed through this operation. The HeII bath temperature was kept constant below 1.6 K without any trouble related to the cryostat. The resultant heat load at 1.6 K was 0.55 W. The total helium consumption rate was 800 cc/h.

Long term operation of superfluid-cooled cryostat for 920 MHz NMR spectrometer

The 920 MHz NMR magnet which successfully generated its designed magnetic field on April 2001 was installed at Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science (NIMS). The magnet again generated 920 MHz without a quench, and has been in continuous operation for over one and a half years up to the present time. The cryostat, which houses the superconducting magnet, employs a pressurized superfluid helium cooling process. Its operating temperature is below 1.55 K. The consumption rates of liquid helium and liquid nitrogen are 0.98 L/h and 0.76 L/h, respectively. Liquid helium is manually supplied every week and liquid nitrogen is automatically supplied every week. Although the cryostat has experienced earthquakes more than 70 times and power failure 3 times, there has been no serious trouble related to the cryostat and the cooling operation is still continuing without interruption.

Tsukuba Magnet Laboratory: Present status and future vision

The Tsukuba Magnet Laboratory (TML) has been a user facility for external users since April 1998 and contracted 91 collaborative studies with external research groups in the 2005 fiscal year. Internal and external researchers use high magnetic fields for magnetic processing as well as extreme-environment measurements. In 2006, two major changes were made to expand the experimental possibilities. One was the replacement of the helium liquefaction system, and the other was the remodelling of the 15 MW DC power supply. TML has also built an NMR complex including a 930 MHz and a 920 MHz NMR spectrometer. We have also started a collaborative study on high-field magnet development with the High Field Laboratory for Superconducting Materials. The projects include the development of a 30 T class superconducting magnet and a 50 T class hybrid magnet.

The measurement and control system for 920 MHz NMR magnet

After the successful test at the Takasago factory of Kobe Steel Ltd (KSL). 920 MHz magnet was transported and installed in Tsukuba Magnet Laboratory (TML), NIMS in April, 2002. To achieve a quick energization and long term operation with a minimum number of operators, the cryostat was equipped with an automated control and monitoring system. During the cooling process below 4.2 K and the energization procedure up to 21.6 T, the temperature of the magnet and He II bath was controlled automatically. Since the all installation procedure has completed in July 2002, the magnet has been continuously cooled to 1.545 K and the temperature variation has been kept within 0.01 K for over a year.

Cu-added jelly-roll Nb/sub 3/Al superconductor with various Nb/Al spacings and compositions

Rapid-heating, quenching, and transformation (RHQT)-processed Nb/sub 3/Al was found to provide high critical current density in high field by Cu addition. There seems to be a difference in the reaction path to A15 between binary Nb/Al (non-Cu-addition) and the Cu added ternary. In the binary case, a Nb/Al composite reacted to form a bcc phase through rapid-heating and quenching (RHQ) treatment and then it was transformed into A15 phase including stacking faults by an 800 /spl deg/C heat treatment. On the other hand, when Cu was added, the composite reacted to form A15 phase including stacking faults through RHQ treatment directly. We fabricated Cu added jelly-roll (JR) Nb/Al wire with various Nb/Al layer thicknesses and compositions and investigated their effect on RHQ process. The Cu added JR wire of Al poor composition for Nb/sub 3/Al stoichiometry showed a behavior similar to the binary. Al rich composition showed a behavior similar to the Cu-addition case. In this work we discussed the Cu addition effect by considering these results.

High- J c Reproducibility of Ag-Sheathed Bi-2212 Tapes

In the fabrication of Ag-sheathed Bi-2212 superconducting tapes, J c reproducibility is obstructed by (1) swelling of the Ag sheath, (2) the rough interface of the sheath and core, (3) cracks in the oxide core, (4) inhomogeneities in composition, particle size, and particle hardness of the raw powder. The swelling is caused by the expansion of dissociated 02 gas within the weak, pure-Ag sheath during the high-temperature melting process; it can be eliminated by using powder calcined in low, partial O2 pressure. Complex, misoriented Bi-2212 layer structures often grow from rough interfaces, which are due to improper deformation processes. Cracks in the oxide core, easily introduced by mishandling, can be significantly reduced to achieve a mechanically stronger AgCu-alloy-sheathed tape. Improvement in high-J c reproducibility and the effects of Cu addition into the sheath on increasing J c and mechanical strength are presented.