1987 Fiscal Year Final Research Report Summary
Saturation Phenomenon of Critical Current Density in Type II Superconductors at High Magnetic Fields
| Project/Area Number |
60420019
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials
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| Research Institution | Kyushu University |
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Principal Investigator |
MATSUSHITA Teruo Kyushu University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90038084)
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| Co-Investigator(Kenkyū-buntansha) |
TOYOTA Naoki Tohoku University, Research Institute for Iron, Steel and Other Metals, Associat, 金属材料研究所, 助教授 (50124607)
OGI Keisaku Kyushu University, Faculty of Engineering, Professor, 工学部, 教授 (40038005)
IWAKUMA Masataka Kyushu University, Faculty of Engineering, Research Associate, 工学部, 助手 (30176531)
TOKO Kiyoshi Kyushu University, Faculty of Engineering, Research Associate, 工学部, 助手 (50136529)
YAMAFUJI Kaoru Kyushu University, Faculty of Engineering, Professor, 工学部, 教授 (90037721)
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| Project Period (FY) |
1985 – 1987
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| Keywords | saturation / flux pinning / critical current density / global pinning force / fluxoid lattice / saturarion / 脱飽和現象 |
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| Research Abstract |
Saturation and nonsaturation phenomena in flux pinning were observed for superconduction Nb-Ta and Nb-Ti containing dislocations and/or normal precipitates as pinning centers. The following facts were clarified.
1. In the case of saturation, the elasticity of the fluxoid lattice increases,while the interaction distance proportional to the yielding strain decreases, according to an increase of the elementary pinning force f_p and/or the pin concentration N_p. The saturation is resulted from compenstion of the two variations in the fluxoid lattice, i.e., hardening and becoming brittle. The mechanism is different from that of the plastic shear assumed in the Kramer model.
2. In the case of nonsaturation, the fluxoid lattice dose not become brittle and an increase of the pinning parameters leads to an increase of the global pinning force. The observed transition from saturation to nonsaturation contradicts the prediction of the Kramer model that the saturated global pinning force is maximum.
3. The proposed avalanching flux flow model insists that the pinning characteristics, saturation and nonsaturation, depends on if the defective fluxoid lattice can be stabilized by the pinning interactions. This model systematically explains the elastic and plastic properties of the fluxoid lattice. It is expected that the nonsaturation can be attained by increasing the pinning parameters up to certain levels.
4. As for the pinning parameter dependence of the nonsaturated global pinning force, Larkin-Ovchinnikov theory predicts F_p N^<2/3>_pf^<4/3>_p, while the linear summation theory insists F_p N_pf_p. The obtained experimental result agrees better with the linear summation theory. This means that an increase of N_p is as effective as f_p for a further improvement of the global pinning force.
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