AC losses in monofilamentary MgB₂round wire carrying alternating transport currents

Abstract

AC losses in a monofilamentary MgB 2 round wire with niobium and copper metal sheaths and carrying alternating transport currents are evaluated at several temperatures and frequencies. First, the transport current losses are observed electrically using a lock-in amplifier. Experimental results show that the AC losses decrease with an increase in the temperature if the amplitude of the transport current normalized by the corresponding critical current is maintained constant. On the other hand, the AC losses increase slightly with the frequency. Next, the AC losses are calculated numerically by a finite difference method. The numerical results for the superconductor filament show a good agreement with the results of the conventional theoretical expression formulated using the Bean model over a wide range of current amplitudes. It is also found that the AC losses in the niobium sheath are negligible whereas those in the copper sheath are comparable with those in the superconductor. On the basis of the numerical calculations, an expression is analytically derived for estimating the eddy current loss occurring in a metal sheath. The derived expression well reproduces the AC loss properties of both the copper and niobium sheaths.

AC Loss Measurements on Multi-Filamentary $ \hbox{MgB}_{2}$ Wires With Non-Magnetic Sheath Materials

“…Limitations in the current leads of the measurement system restricted the measurements to below 200 A. In [13] a linear approximation is suggested for the critical current up to 35 K. The results for the rectangular sample indicate linearity up to approximately 35.5 K, and an extrapolation is used to determine the critical current at 33.5 K, the lowest temperature used in the following AC loss measurements on that sample. …”

“…with simultaneously applied magnetic fields and transport currents at variable temperatures, are necessary. In the literature AC loss measurement results due to either AC transport currents [13], [14] or AC applied magnetic fields [14]- [16] have been reported.…”

Electromagnetic behaviors of superconducting Nb3Sn wire under a time-dependent current injection

“…2 In recent years, attempts have been made to study the electromagnetic behaviors of some superconductors by numerical simulation. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] As for finite element modelling (FEM), the extreme complexity of hierarchical geometry and structure of Nb 3 Sn strand and CICC requires a special concern for the modelling of the strand entity. Therefore this will inevitably consume large amounts of CPU time and memory capacity in meshing and calculating process.…”

“…So, 2D simulations mainly focus on high-temperature superconductors (HTS) with homogenous material and standard bulk shape. 3,4,6,[8][9][10][11][13][14][15] As the advance of computer technology, it becomes feasible to use FEM to cope with Nb 3 Sn strand at the cost of long-time computation and large memory. Even so, modelling the strand down to filament level is still troublesome.…”

Proposal of new structure of MgB2 wires with low AC loss for stator windings of fully superconducting motors located in iron core slots

“…The AC losses in a MgB 2 monofilamentary wire carrying alternating transport currents have been evaluated at several temperatures and frequencies so far [2]. By combining the numerical calculations with a finite difference method and the theoretical analysis for an eddy-current loss in a metal sheath with low resistivity, the experimental results have been reproduced very well and the physical mechanism of AC losses in the MgB 2 monofilamentary wire has been revealed clearly [3]. The numerical technique to evaluate the AC losses in the stator windings located inside the iron cores has also been proposed, and the numerical results with a finite element method have suggested that it would be very promising to develop the stator windings for liquid hydrogen pump with low loss and high efficiency even compared with copper windings cooled down to liquid hydrogen temperature of about 20 K [4].…”