Magnetization and Critical Currents of NbTi Wires with Fine Filaments
In high energy accelerators such as the SSC, the magnetization of the superconductor is an important component in determining the harmonic fields at injection (~0.3T). In an effort to reduce these residual fields, interest has focused on NbTi conductors with fine filaments which are expected to have a reduced magnetization as dictated by the critical state model. With this in view, the magnetization and critical currents were measured at 4.3K for a set of NbTi wires with filament diameters, d, ranging from 1.0 to 5.0 microns. The data show that, although the magnetization scales linearly with d, it does not do so with the product Jc d for d less than 3 μm. However, at these d values, the critical transport current density, Jc, of NbTi was observed to decrease rapidly as a function of d. The origin of this Jc degradation and its effect on the scaling of magnetization within the framework of the critical state model is explored. We also examine the question of the observed asymmetry of the hysteretic magnetization.
KeywordsCritical Current Magnetization Loop Fine Filament Critical State Model Filament Diameter
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