IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006 1547 Development of a Superconducting Joint for High Field NMR T. Fukuzaki, H. Maeda, S. Matsumoto, S. Nimori, S. Yokoyama, and T. Kiyoshi Abstract—The innermost coil of a new high-field NMR magnet such as a 1-GHz NMR magnet is designed by using a new super- conductor. It is therefore important that a superconducting joint between the new superconductor and the conductor was de- veloped. We have developed a new superconducting joint method for the conductor, which is expected to be used for the in- nermost coil of the 1-GHz NMR magnet. This joint method uses the layer that is formed on the matrix surface of the conductor. This layer enables the soldering of the conductor; thus, it is possible to solder the con- ductor and conductor. The superconducting property of the joint that is joined by the superconducting solder (for example, solder) showed good performance under a magnetic field of 0.1 T. Index Terms— conductor, superconducting joint, 1-GHz NMR. I. INTRODUCTION A HIGH-SENSITIVITY and high-resolution NMR magnet, such as a 930-MHz NMR [1], is constructed using mul- tiple and superconducting magnets. Each magnet is joined in a series by a superconducting joint between the conductor and the conductor (or the NbTi con- ductor) and is usually operated in the persistent mode. An NMR magnet with a sufficient magnetic field stability (for example, field decay 10 Hz/h) is required for NMR measurement. It is necessary that the resistance of the superconducting joint be low for the persistent current decay. The superconducting joint method between the conductor and the conductor has been used “solder dip method” thus far [2]. It is carried out as follows: first, the alloy matrix of the and conductors is removed using a dip of molten tin and the naked and filaments are dipped with the solder, which is superconducting at 4.2 K. For a new high-field NMR magnet such as a 1 G-Hz NMR, which is developed by NIMS and RIKEN, the inner coil is de- signed by a new superconductor instead of the bronze processed Manuscript received September 20, 2005. This work was supported in part by the RIKEN Structural Genomics/Proteomics Initiative (RSGI), the National Project on Protein Structural and Functional Analyses, Ministry of Education, Culture, Sports, Science and Technology of Japan. T. Fukuzaki and H. Maeda are with the RIKEN Genomic Science Center, Yokohama 230-0045, Japan (e-mail: fukuzaki@gsc.riken.jp). S. Matsumoto, S. Nimori, and T. Kiyoshi are with the National Institute of Materials Science, Tsukuba 305-0003, Japan. S. Yokoyama is with the RIKEN Genomic Sciences Center, Yokohama 230- 0045, Japan and the RIKEN Harima Institute, Spring-8, Hyogo 679-5148, Japan and is also with the University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan. Digital Object Identifier 10.1109/TASC.2006.870842 Fig. 1. The cross sectional image of the RHQT processed supercon- ductor. conductor. It is therefore important that a supercon- ducting joint between the new conductor and the con- ductor be developed. A rapid heating, quenching, and transfor- mation (RHQT) processed conductor [3]–[5] is an effec- tive superconductor for the inner coil of a 1 GHz NMR magnet. However, the conductor has a cross section structure with the matrix that is not corroded by acid or alkali. Con- sequently, the solder dip method does not apply to the conductor because the removal of the matrix is difficult. The development of a new superconducting joint method between the conductor and conductor is necessary. We have developed a new method for constructing an superconducting joint using the solder without removing the matrix of the conductor. In this paper, we report the method of the superconducting joint, the opti- mization of joint treatment, and the superconducting property of a joint part. II. EXPERIMENT A. Sample and Experimental Method Fig. 1 shows a cross sectional image of an RHQT processed conductor before the final heat treatment at 800 for 10 h. The size of the conductor is 1.8 mm 0.8 mm. Several alloy filaments are arranged in the matrix, and the outer side is clad by for stabilization. The conductor is converted from an alloy to a superconductor, with the heat treatment at 800 for 10 h. On the other hand, the size of the conductor is 0.5 mm, the filament number is 1536, and the matrix of the conductor is . The cross section of the joint part was observed using a scan- ning electron microscope (SEM). The composition analysis was carried out with an energy dispersal spectroscope (EDS). The 1051-8223/$20.00 © 2006 IEEE