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Saturation Phenomenon of Critical Current Density in Type II Superconductors at High Magnetic Fields

高磁场下II型超导体临界电流密度的饱和现象

基本信息

批准号：
60420019
负责人：
MATSUSHITA Teruo
金额：
$ 15.87万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (A)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1987
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-60420019/
关键词：
saturation flux pinning critical current density global pinning force fluxoid lattice saturarion 脱飽和現象 Kramer則

项目摘要

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.

以超导Nb-Ta和Nb-Ti位错和/或正常析出相为钉钉中心，观察到钉钉过程中的饱和和非饱和现象。以下事实得到澄清。饱和情况下，随着基本钉钉力f_p和钉钉浓度N_p的增大，流态晶格的弹性增大，而与屈服应变成正比的相互作用距离减小。饱和是由于流体晶格的两种变化的补偿，即硬化和变脆。其作用机理与Kramer模型中假设的塑性剪切不同。在非饱和情况下，流态晶格不会变脆，钉钉参数的增加导致整体钉钉力的增加。观测到的从饱和到非饱和的转变与Kramer模型的预测相矛盾，即饱和的整体钉住力最大。所提出的雪崩通量流模型认为，钉住特性（饱和和非饱和）取决于钉住相互作用是否能稳定缺陷的类流体晶格。该模型系统地解释了流态晶格的弹性和塑性特性。将钉钉参数提高到一定水平，可望达到不饱和状态。对于非饱和全局钉钉力的钉钉参数依赖性，Larkin-Ovchinnikov理论预测F_p N^<2/3>_pf^<4/3>_p，而线性求和理论则预测F_p N_pf_p。得到的实验结果与线性求和理论吻合较好。这意味着N_p的增加与f_p的增加对进一步提高全局钉住力同样有效。