パウダー·イン·チューブ法MgB2テープ線材における歪効果

Abstract

We investigate the influence of lengthwise mechanical strain on the critical current (Ic), the strain effects, for three kinds of “powder-in-tube (PIT)" route MgB2 conductors. We tested in situ monocore MgB2/iron, ex situ monocore MgB2/stainless steel, and ex situ 14-filament MgB2/nickel tapes. Ic was measured for each sample as a function of lengthwise external strain in magnetic fields (B) at 4.2, 15, 20, and 25K using a U-shaped rig made of stainless steel. Even though the fabrication process and conductor configuration (number of filaments, width, and thickness) are different, the Ic-strain relations were essentially the same in all MgB2 samples. By increasing the strain, large and irreversible degradation occurred after linear and reversible Ic-strain relation up to the maximum of Ic (Icm). The slope of linear Ic-strain relation in the reversible regime, d(Ic/Icm)/d(strain), depends on both temperature and magnetic field. We discuss the relations between d(Ic/Icm)/d(strain) and magnetic fields normalized by the irreversibility field (Birr.) We also examined the strain effect of ex situ PIT monocore in Nb3Sn/stainless steel tape. The Ic-strain relation obtained is a parabolic one that has been reported so far for many kinds of multifilamentary Nb3Sn conductors. This indicates that the linear strain dependence of Ic in MgB2 conductors is an essential feature of MgB2.