Persistent current joints between technological superconductors

Abstract

Persistent current joints are crucial components of superconducting magnets—enabling the production of the high and ultra-stable magnetic fields required, for instance, for magnetic resonance measurements. At this critical juncture when persistent mode magnets containing commercial high temperature superconductors may soon become a reality, it is of value to take stock and evaluate current challenges faced in the field of jointing. This paper provides a review of progress made to date on the production and characterization of joints between the five major technological superconductors—NbTi, Nb3Sn, MgB2, BiSCCO and REBCO, including the materials that are used to make these joints.

NMR of Macromolecular Assemblies and Machines at 1 GHz and Beyond: New Transformative Opportunities for Molecular Structural Biology

“…HTS technology has very recently advanced to the stage where these materials can be used to generate reasonably stable and homogeneous magnetic fields for NMR. Beyond the development of HTS materials, challenges of the magnet technology have included jointing between the HTS and LTS coils (20) and field homogeneity, further discussed below. Furthermore, the addition of HTS coils creates a spatial challenge.…”

Growth and superconductivity of niobium titanium alloy thin films on strontium titanate (001) single-crystal substrates for superconducting joints

“…Recently, the REBCO high-temperature superconductors have been expected to be used in high-magnetic-field magnetic resonance imaging (MRI) equipment 3 – 5 . One of the technologies required for high-magnetic-field MRI is the joint technique of REBCO-coated conductors (CCs) 6 . In the direct joint method connecting REBCO superconducting layers in the REBCO CCs, the joint structure is simple.…”

“…In the direct joint method connecting REBCO superconducting layers in the REBCO CCs, the joint structure is simple. However, a complicated joining technique and long processing time are required because the superconducting properties of REBCO are strongly affected by the directions of REBCO crystals and the oxygen content in REBCO 6 – 8 . In contrast, the indirect joint method connecting the REBCO layers in the CCs via another material can avoid the problems of the direct joint method.…”

“…However, a large joint area is necessary for a low-resistance circuit because Ag and Cu are not superconductors, although they have low resistivities (0.2–0.3 × 10 −8 Ωm at liquid nitrogen temperature) 13 . In order to achieve low resistance varying from 10 −13 Ω to 10 −14 Ω, which is required for operating MRI in a persistent current mode 6 , in the case of a Ag layer having a thickness of 10 μm and width of 5 mm, the joint area is calculated to range from 0.6 m 2 to 6 m 2 , i.e., the joint length ranges from 120 m to 1200 m at liquid nitrogen temperature. Therefore, in the indirect joint method, the joint material should be a superconductor.…”

Fabrication of NbTi superconducting joint by electromagnetic forming method

“…Among them, cold-pressing is comparatively convenience. However, the evidence of an oxide layer and residual Cu-rich particles at poorly bonded interfaces in the cold-pressing joint had been confirmed [10,11]. In order to enhance the electrical performance of coldpressing joint, a new jointing method should be found to prevent the negative influence of the oxide film during jointing process.…”