1PO5-40 A 7.09 T High-T_c Trapped Field Magnet Made of Two Non-irradiated YBCO Bulks

Huaming Wen 1, Liangzhen Lin 1, Liye Xiao 1, Lin Xiao 2, Yulei Jiao 2, Minghui Zheng 2, Hongtao Ren 2. 1 Laboratory of Superconducting Electrical Engineering, Institute of Electrical Engineering, Chinese Academy of Sciences (LSEE, IEE, CAS), Beijing 100080, China. 2 General Research Institute for Non-ferrous Metals (GRINM), Beijing 100088, China.

Presenting Author: H. Wen

A trapped field magnet of 7.09 T at 29.8 K was achieved when applied field reached 8 T by FC way. It was made of two non-irradiated YBCO bulks provided by GRINM. The charging procedure, the creep of the magnet and it mechanical performance were investigated. About 90% of the applied field was trapped. But the magnet was broken when the applied field is higher than 10 T.

1PO5-41 The Study of YBCO Trapped Field Magnets

Ling Xiao 1, Hongtao Ren 1, Yulei Jiao 1, Minghui Zheng 1, Huaming Wen 2, Shanlin Li 3, Xiunian Jing 3, Li Lu 3, Liang-zhen Lin 2. 1 General Research Institute for Non-ferrous Metals, Beijing 100088, China. 2 Institute of Electrical Engineering, Chinese Academy of Sciences (CAS), Beijing 100080, China. 3 Institute of Physics & Center for Condensed Matter Physics, Chinese Academy of Sciences (CAS), Beijing 100080, China.

Presenting Author: L. Xiao

The single domain YBCO superconducting bulks with diameter of 18~30mm were made by the melt textured growth and top seeded method. The trapped field was measured by using a Hall probe on the surface of the bulk at applied fields of 5~10T and 30~77K. For two superconducting bulks with 26mm in diameter and 11mm in thickness, a trapped magnetic field of 7.1T was achieved at the 3mm gap between two bulks (without irradiation) at about 30K after activated by the magnetic field of 8T. A larger magnetic pressure cracks superconducting bulks when the applied fields excess 8T. The obvious cracks were observed on the surface of bulks. A 2D axial Hall probe sweep was used to mearsure the field mappings of frozen flux distribution on the surface of samples. The results showed that the maps were single peak and multiple peaks before and after high magnetic field activation, respectively. The effects of temperature, time and the diameter of bulks on the trapped field as well as the degeneration of trapped field with time were also investiated.

1PO5-42 Numerical Evaluation of Stresses in A Bulk HTS in Field Cooled Magnetization

M. Tsuchimoto, Hokkaido Institute of Technology, 7-15, Maeda, Teine-ku, Sapporo 006-8585, Japan

Presenting Author: M. Tsuchimoto

A trapped field magnet (TFM), or a bulk high T_c superconducting magnet, is one application of a melt processed bulk high T_c superconductor (HTS). Magnetic field, which is greater than a few teslas, can be trapped in the HTS when shielding currents are large enough. In addition to large shielding currents, strength of the material is also important to obtain strong trapped field magnet since large stresses caused by Lorenz force between the shielding currents and the trapped field. There are some destructive experiments of the TFM to evaluate the strength of the material. The 1 dimensional analysis of stresses was well evaluated analytically by Y. Ren and R. Weinstein et. al. In the present paper, the problem is solved numerically with finite difference method. Numerical solutions agree with analytical solutions in the 1 dimensional problem. Dependence of shielding current on magnetic field is considered in the numerical analysis. Difference of 1 dimensional and 2 dimensional problems are also discussed, and comparison with experimental results are shown in the paper.

1PO5-43 The use of a thermobaric analyzer at synthesis of the superconductor Hg-1223 and HgCaO₂ inside a sealed quartz tubes

Alfredo G. Cunha 1, Marcos T.D. Orlando 1, Francisco G. Emmerich 1, and Elisa Baggio-Saitovitch 2. 1 Departamento de Física, Universidade Federal do Espírito Santo, 29060-900 Vitória-ES, Brazil. 2 Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Siguad 150-Urca, 22290-180 Rio de Janeiro-RJ, Brazil.

Presenting Author: A.G. Cunha

In this work we compare the pressure inside sealed quartz tubes versus temperature plot for two different syntheses. One synthesis was correlated to a superconductor HgBa₂Ca₂Cu₃O_8+d (Hg-1223) sample and the other to the competitor impurity phase HgCaO₂. This study was done by using a new technique called thermobaric analysis (TBA), which was developed by us and allows the in-situ measurement of the total pressure of the gases in sealed quartz tubes during the syntheses at high temperatures. When the pressure versus temperature curve for superconductor synthesis is compared with that of HgCaO₂, it is possible to see the competition at the formation between the superconductor and the HgCaO₂, and the plot shows the temperature interval in which the superconductor synthesis pressure is lower than HgCaO₂. The superconductor sample synthesized at this temperature region showed a monophasic character with T_c = 133 K without post-annealing.

1PO5-44 Crystal Nucleation Period and Silver Distribution in Isothermal Solidification of Y_1.8Ba_2.4Cu_3.4O_y/Ag System

Chuanbing Cai, Kaori Tachibana and Hiroyuki Fujimoto, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji 185-8540, Japan

Presenting Author: C. Cai

Crystal growth with and without top seeding technique is studies in an isothermal solidification of Y_1.8Ba_2.4Cu_3.4O_y with the additions of 10wt% Ag and 0.5wt%Pt. The textured domains are achieved at various lower maximum processing temperature(T_max) down to 1000?. Different crystal nucleation mechanisms exhibit preferably in order of time. Compared with the seeded sample, the non-seeded sample costs a longer time for the first grown domain to occur after a constant undercooling is performed. The initial nucleation period is closely related to undercooling and Tmax. The understanding of nucleation chronology is instructive not only to single-domain growth, but also to uniform distribution of trapped hetrogeneous particles in Y(RE)BaCuO/Ag system.

In present work, the trapped silver particles in YBaCuO grown domain is also studied. Its distribution strongly depends on the undercooling, while the variation of Tmax produces no significant influence. At melt stage, silver particle acts as second liquid phase and then is trapped in the monotecto-peritectic reaction of YBaCuO possibly by Uhlmann-Chalmers-Jackson type.

1PO5-45 Reduction of porosity in RE123 pseudo crystals

Makoto Kambara, Hari Babu Nadendla, Yunhua Shi, and David A. Cardwell, Department of Engineering, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom

Presenting Author: M. Kambara

It has been recognized that RE₂BaCuO₅ (RE-211) particles, which supply the RE solute needed for the crystal growth through liquid, act as inclusions and exhibit the particle pushing behavior during solidification of RE₁Ba₂Cu₃O_y (RE-123) superconducting oxides. Recently, these Y211 particles were found to decrease the effective liquid diffusion area and can terminate the solidification when they accumulate sufficiently ahead of the growth interface. Similarly, it is considered that any air gap in the 211+L semi-solid melt could also act as inclusions and cause the pseudo crystal to stop growing in the same manner as the Y-211 particles. Finally, pores within the RE123 crystals can effect both the superconducting properties and the mechanical properties of the 123 crystals. Hence it is essential to reduce the volume of pore within the pellet for the purpose of obtaining large single domain crystals. The aim of the present work is to reduce the size and density of pores in the RE-123 psuedo crystals. Uniaxially pressed precursor pellets were sintered in a vacuum at around the temperature where the liquid phase appears prior to solidification processing. RE-123 pseudo crystals were grown using these pellets by the hot seeding technique. The relationship between the microstructures observed and the key process and experimental variables is discussed.