MgB₂cylindrical superconducting shielding for cryogenic measurement applications: a case study on DC current transformers

Abstract

A method for designing cylindrical hollow superconducting shields for cryogenic measurement devices operating in background fields of 1 T is proposed. The shield design is based on MgB2 composite, manufactured by the reactive Mg liquid infiltration process [1]. The MgB2 composite allows low-cost shields with good mechanical resistance to be realized easily. The geometrical design is benchmarked by the experimental characterization at 4.2 K. A design case study for the shield of a cryogenic DC current transformer is reported. Design results show a shielding efficiency of 70% for both the axial and radial components, with prospective measurement accuracy up to 10 ppm on 100 kA.

Magnetic Shielding Above 1 T at 20 K With Bulk, Large Grain YBCO Tubes Made by Buffer-Aided Top Seeded Melt Growth

“…Bulk cylinders made of high temperature superconductors (HTS), on the other hand, have already demonstrated their high-field shielding abilities. At T = 4.2 K, fields of the order of 1 T can be shielded with bulk MgB2 [3,15,16] and efficient shielding up to 2 T was reported for a long MgB2 cylinder [17]. These values are comparable to those achieved with using Nb-Ti multifilamentary composite wires at the same temperature [18].…”

“…Several high sensitive scientific devices, e.g. superconducting quantum interference devices [1,2], dc current transformers [3], or cryogenic current comparators [4], need to be protected against the magnetic field environment and therefore must be shielded. Superconducting materials are certainly the best candidates to build passive magnetic shields at low frequency.…”

Design, Assembly, and Commissioning of a Cryogenic DC Current Transformer Designed for Measuring Currents of up to 80 kA

“…Primary bus-bar off-centering is addressed using an iron magnetic shield. Sensitivity to external magnetic field, due also to the return bus-bar, is minimized by means of a cy lindrical superconducting shield made of MgB 2 composite [16]. In Fig.…”

“…The design of the superconducting shield is described in [16] and the final object is being produced [24].…”

“…The proposed sensor is based on: An optimized geometrical design of the sensing element, exploitation of a magnetic alloy suitable for cryogenic applications (referred to as cryogenic permalloy), and mitigation of cores saturation through a combination of ferromagnetic and superconducting shield [16]. As proof of concept, the characterization of a demonstrator rated at 20 kA was described.…”