Low field critical current density of titanium sheathed magnesium diboride wires

Abstract

Low field critical current density of titanium sheathed magnesium diboride wires (MgB2) is replacing some of the conventional superconductors due to its low cost and availability in kilometer lengths. MgB2 has also been considered for AC applications. In order to model the AC losses and the critical currents of the applications, intrinsic Jc(B)-dependence is an important factor also at low fields. In this work Jc(B)-dependence of an MgB2 sample is extracted from the standard in field voltage-current measurements. The proposed method is applied to a non magnetic titanium sheathed sample at 16 and 20 K and a simple formula for Jc(B) aligns with the measurements. In the fitting process, the critical current distribution inside the wire is numerically simulated in order to take the self field of the sample into account. Moreover, the same formula aligns with measurements of a different sample. These critical current measurements, performed at 4.2 K, were based on magnetization. In the self field computations, the superconducting cross section must be determined accurately. Therefore, we tailored an image processing tool for MgB2 wires to obtain the geometry from a photograph. IntroductionSince the superconductivity of magnesium diboride (MgB 2 ) was discovered in 2001 [1], the pursuit for high performance conductors started and currently these conductors are commercially available in kilometer lengths. The advantages of these wires are relatively low price and their suitability for cryocooled applications whose temperature range is between 12 to 30 K [2]. Therefore, they are expected to replace some of the conventional superconductors. The wires are becoming more attractive also for AC use, which is due to the higher operation temperature, and thus improved stability compared to LTS wires.In case of MgB 2 , there are plenty of suitable candidates for cheap matrix metals, which do not react with MgB 2 . However, they must also fulfill the mechanical, thermal, and electromagnetic requirements for a specific application. For AC applications, hysteretic materials, for example Iron and Nickel, are excluded. However, Titanium is a promising nonmagnetic sheath material, because of its mechanically excellent properties and the lightness [3,4].The AC losses depend on the intrinsic J c (B)-characteristics of superconductor [5]. Unlike in DC applications, the J c (B)-dependence has to be taken into account for the whole AC cycle, also at the low field values. In addition, J c (B)-curves provide valuable information on the quality of superconductor and on its pinning properties [6]. Therefore, we apply and develop

Study of the potential of three different MgB2tapes for application in cylindrical coils operating at 20 K

“…In this case, the measured I c (B) data can be fitted e.g. by a computed curve [64] based on the modification of the Kim [65] and Anderson [66] models. However, this is only a mathematical problem which requires enhanced attention in the future [67].…”

Numerical modeling of MgB2 conductors for high power AC transmission

“…where E c =10 -4 V/m, n=40 and J c (B) is the critical current density obtained from the experimental characterization of MgB 2 wires at 20 K for fields up to 1.7 T [9]: 1). The available data (see textbook [10] and references therein) were uploaded and interpolated by the software Comsol Multiphysics, where the FEM model was implemented.…”