Niobium-titanium (Nb-Ti) superconducting joints for persistent-mode operation

Abstract

Superconducting joints are essential for persistent-mode operation in a superconducting magnet system to produce an ultra-stable magnetic field. Herein, we report rationally designed niobium-titanium (Nb-Ti) superconducting joints and their evaluation results in detail. For practical applications, superconducting joints were fabricated by using a solder matrix replacement method with two types of lead-bismuth (Pb-Bi) solder, including Pb42Bi58 as a new composition. All the joints attained a critical current of >200 A below 1.43 T at 4.2 K. Our optimized superconducting joining method was tested in a closed-loop coil, obtaining a total circuit resistance of 3.25 × 10−14 Ω at 4.2 K in self-field. Finally, persistent-mode operation was demonstrated in an Nb-Ti solenoid coil with a persistent-current switch. This work will pave the way to developing high-performance Nb-Ti superconducting joints for practical applications.

7 T Niobium-Titanium-Based Persistent-Mode Superconducting Magnet for an Electron Beam Ion Source

“…Specifically, five superconducting joints were applied to connect the magnet coils, and two joints were utilized to make a closed circuit between the PCS and the magnet. Our superconducting joint technology has been reported in a previous study [22].…”

“…Because the high inductance of the magnet for EBIS causes a long current charging time, it is necessary to improve the operation efficiency by applying the persistentmode. If an Nb-Ti magnet also adopts the persistent-mode in an LHe recondensing-type cryostat, it would considerably reduce the operational cost of the system and the heat input into the cryostat [18], [19], [22].…”

Superconducting Joining Concept for Internal Magnesium Diffusion-Processed Magnesium Diboride Wires

“…High-performing superconducting joints will be essential to employing IMD-processed MgB 2 conductors in future MRI systems, however. , This is because MRI magnets are usually operated in the persistent mode to produce an ultrastable magnetic field with a decay rate of <0.1 ppm h –1 . For operating a superconducting magnet in the persistent mode, the two ends of the magnet must be short-circuited using superconducting joints, so that current can flow in a closed-loop . Since the invention of an IMD processed MgB 2 conductor in 2003, there has been only one report on superconducting joints using practical scale IMD-processed MgB 2 wires (i.e., ∼1 mm in diameter) .…”

High-temperature-tolerable superconducting Nb-alloy and its application to Pb- and Cd-free superconducting joints between NbTi and Nb3Sn wires

“…To date, Pb-Bi and Wood's metal (50% Bi, 26.7% Pb, 13.3% Sn, and 10% Cd) have served as superconducting intermedia to join separated superconducting wires to each other in NMR magnets [1,2]. Pb-Bi and Wood's metal have relatively high critical magnetic fields (B c2 ) of more than 1.5 [3][4][5] and 1.0 T [6] at the liquid helium temperature, respectively. These superconducting solders are now indispensable materials, especially for achieving superconducting joints between NbTi and Nb 3 Sn wires in high-field NMR magnet systems [1,2].…”