ブロンズ法Nb₃Sn多芯線の交流損失に及ぼす錫拡散防止層の影響

1. 直流磁界に小振幅変動磁界が重畳された場合の履歴損失

抄録

A bronze-processed Nb₃Sn wire with a Nb barrier protecting Cu stabilizer from Sn diffusion contains a superconducting hollow cylindrical layer of Nb₃Sn inside the barrier. Moreover a Nb₃Sn superconducting layer in each filament is hollow cylindrical, too. In this paper the expressions for the magnetizations and hysteresis losses for this type of wire were derived in the case where a transverse AC magnetic field of trapezoidal wave form with a small amplitude was superposed to a DC bias magnetic field. The present expressions were compared with our experimental results and both of them agreed well with each other over a wide range of the DC bias field.
The hysteresis losses of a Nb₃Sn wire with a Nb barrier is mainly subjected to the magnetizations of a superconducting cylinder inside the Nb barrier, and amounts to several times larger than that with a Ta barrier. It is also pointed out that the values of critical current densities of superconducting barrier and superconducting filaments which contribute to the magnetization are usually different from that estimated from the critical current measurement by a resistive method, while the magnetic field dependences are nearly the same.