Hisao Nonoyama

Preparation of Bi-Sr-Ca-Cu-O Superconducting Fibers by Laser Pedestal Growth Method

2212 BiSrCaCuO superconducting fibers were prepared by the laser pedestal growth method. The influence of fiber diameter and growing speed on microstructures and superconducting properties was investigated. Temperature gradient and growing speed were important factors in obtaining highly aligned micro-structures. The temperature gradient increases as the fiber diameter decreases. So highly aligned structures were obtained when the fiber diameter was small and the growing speed was low. When the nominal diameter of grown fiber was 0.5mm and the growing speed was 30mm/h, Jc of 17,500A/cm2(77.3K, 0T) was obtained. In the case of small fiber diameter, aligned crystal structures and relatively high Jc’s were maintained in spite of the high growing speed.

2.3kA BSCCO Rod Grown by Laser Pedestal Growth Method

Bi2Sr2CaCu2Ox superconducting rods were grown by the laser pedestal growth method.The samples were 4mm in diameter and 150mm in length. The critical current for DC and AC at 4.2K have been attained to be 2.3kA and 4.6kAp, respectively. The AC losses at 50Hz and 77.3K were also examined by using transport technique. The AC loss of 4.4W/m at 400Ap-50Hz operation is enough low for a current lead application in comparison of the copper joule loss.

Preparation and Characterization of Superconducting Fibers Grown by Laser Pedestal Growth Method

Bi2Sr2CaCu2Ox superconducting fibers were prepared by laser pedestal growth method. Laser pedestal growth method is one of the directional solidification method. Important parameters for alingment in the crystal growth are temperature gradient at solid-liquid interface and the growing rate. The effect of the two parameters to the critical current density was investigated. As it is important to keep the uniformity of the diameter to prepare a long fiber, the auto-diameter-control system with fuzzy function was investigated. With the system, 370μm fiber was prepared and measured the superconducting characters.

Microstructure and Jc of BiSrCaCuO Superconducting Fibers Prepared by Laser Pedestal Growth Method

BiSrCaCuO Superconducting fibers were prepared by laser pedestal growth method using a focused CO2 laser. The relationships among microstructure, Jc-B, and post-growth treatments, were investigated using the fibers prepared at 30mm/h of growing speed. As-grown structures were mainly consisted of aligned 0112 phase and 2201 phase. Aligned 2212 superconducting phase was created along the alignment of 0112 phase after post-annealing. When samples were annealed under tensile force, structures observed by optical microscope became dense and nearly single 2212 phase even at short time annealing, but non-superconducting phases that are sub-micron order size, stacking faults were observed by transmission microscope. Non-superconducting phases were increased when the starting composition was changed from 2212 to 0112. Jc-B characteristics were improved by combination of tension annealing and the change of starting composition.

Properties and Application of High Ic Bi Based Oxide Superconductors Prepared by Laser Pedestal Growth Method

Bi2Sr2Ca1Cu2Ox Superconductors were prepared by laser pedestal growth method. Annealing conditions were investigated to increase Jc and the diameter dependence of Ic was studied to increase Ic. The best annealing condition was 840° C*more than 500 hours. When the diameter was 3.0mm, Ic=500A was obtained. Also, electric current was applied to a sample in liquid helium or with the one electrode of a sample in liquid helium and another over liquid helium as a current lead situation. Oxide superconductor will be thought to be useful for current lead on a superconducting magnet in liquid helium. The possibility of application for it was investigated. In liquid helium, 1000A current could be applied without quenching. But in current lead situation, there was increasing of the generated voltage at the upper electrode with more than 450A current.