K. Hayakawa

Publications (2)2.08 Total impact

• Article: Flux pinning in Nb-Ti composite superconductors having artificial normal pins with different coherence length

  K. Hayakawa, Y. Zhu, O. Miura, D. Ito
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  ABSTRACT: Recently, improvement of the flux pinning properties in several kinds of superconductors has been achieved by introducing artificial pinning centers (APC). The artificial pinning technique is very useful not only to increase critical current densities J_c but also to study the pinning mechanism and its optimization. We have been developing APC composites for the purpose of improvement in magnetic field dependence of J_c for Nb-Ti superconductors. In this study, we investigate the temperature and magnetic field dependence of the pinning force density F_p for Nb-Ti multifilamentary composites having superconducting pins (Nb) and normal conducting pins (Cu, Cu-Ni) with different coherence length ξ_n. The F_p obtained for all APC wires is larger than that for conventional wire without APC, and the F_p increases as the pin size decreases. In spite of the same APC arrangement in the design stage, F_p for Cu-Ni pin wire is larger than that of Cu pin and also the F_p's values for the normal pins are smaller than that of superconducting Nb pin wire. Furthermore, T_c for the normal pin wires reduces drastically with reducing pin size, and the peak field of the F_p dose not shift to higher field, while that for Nb pin dose. We evaluate the elementary pinning force f_p for these APC wires using the G-L theory taken into account the proximity effect
  IEEE Transactions on Appiled Superconductivity 04/2001; · 1.04 Impact Factor
• Article: Characteristics of normal conducting artificial pins in Nb-Ti multifilamentary composites

  Y. Zhu, O. Miura, K. Hayakawa, D. Ito
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  ABSTRACT: In order to reveal flux pinning characteristics for different pinning materials in superconductors, Nb-Ti multifilamentary composites having different materials, Nb, Ta, Cu-Ni and Cu introduced as artificial pinning centers (APC) were studied, Magnetization was measured to analyze critical temperature T_C and to obtain magnetic field dependence of pinning force density F_P. The F _P properties for APC are different from each other, in spite of almost the same design of pins. A simulation for the distribution of superconducting order parameter using a S-N multilayer model under a significant proximity effect was carried out on the basis of the G-L theory. The flux pinning properties calculated from the order parameter simulations were compared with those of experimental results. Qualitative agreement between them was obtained
  IEEE Transactions on Appiled Superconductivity 04/2001; · 1.04 Impact Factor