External field effect on the current distribution in superconducting composites: evaluation of the degradation in adiabatic conditions

Analytical Field Calculations for Various Helical Conductors

“…The current distributions within superconducting multi-filamentary composites have been discussed using the continuum model in which a composite is assumed to be a perfect mixture of superconducting filaments and a matrix of normal metal, replacing the filamentary discrete arrangement with a concentric cylindrical layer [7]. According to the above-mentioned method, and together with the assumption that the current distribution within each filament is uniform (the filament model), the current distribution among each filament within a composite can be analyzed, reflecting the filamentary structure.…”

Stabilization for thermomagnetic instability of CuNi/NbTi superconducting wire in spatially distributed magnetic field

“…A method of stabilizing the CuNi/NbTi superconducting wire in the distributed magnetic field by adjusting the twist pitch of the higher-order stranded conductor, that is, by utilizing the longitudinal magnetic field effect, has been presented. The condition for the uniform distribution of the current in the strand, which is derived under the assumption of a uniform magnetic field [3], is shown to be effective in stabilizing the wire in the presence of a distributed magnetic field. It is seen that special caution is required in the case of the distributed magnetic field when the longitudinal magnetic field component (average value) is high, since the distributed magnetic field instability occurs more easily.…”

“…Funaki and colleagues [3] derived the current density distribution in the strand by assuming that the effect of the perpendicular magnetic field can be ignored, since the filament radius is sufficiently small [4]. When the transversal magnetic field effect is ignored, the current distribution in the nonsaturated region becomes uniform, and the current density j r is given as follows as a function of time:…”

“…In this section we consider (6 + 1) 3 twisted wire in which CuNi/NbTi strands with the same specifications as in Table 1 are arranged ideally as in Fig. 4.…”

“…A method was earlier proposed to reduce low magnetic field instability and longitudinal magnetic field instability by adjusting the twist direction and the twist pitch (i.e., the longitudinal magnetic field) [3]. This is called the longitudinal magnetic field effect.…”