Joint Design and Test for the SCH

Abstract

The NHMFL Series Connected Hybrid (SCH) magnet will provide an energy-efficient 36 T to the DC user facility by employing a 20 kA superconducting outsert coil in series with a resistive insert. The magnet outsert consists of three concentric layerwound sub-coils using three different grades of Nb 3 Sn Cable-inConduit Conductors (CICC). The electrical joints in the superconducting outsert require low DC resistance to minimize the refrigeration requirement at the operational 4.5 K temperatures and low AC losses to ensure good stability against ramping operation required by the users. There are four internal splice joints in the outsert, which are Nb 3 Sn to Nb 3 Sn joints with the same design configuration. There are another two terminal joints between the Nb 3 Sn outsert and the two NbTi buslines, which connect the outsert terminals to the two current leads. The two Nb 3 Sn to NbTi terminal joints are of identical configurations. All of the joints will be praying-hands configuration with an operation current of 20 kA. The R&D for the joins has been carried out at the NHMFL. The joints design and test results are discussed in this article.

Fabrication of the Nb3Sn/Cu CICC Coil and Cold Mass for the Radboud University HFML 45 T Hybrid Magnet

“…Additional conductor and coil design details are provided in [4]. The splice joints and termination joints have sintered connections formed during the reaction heat treatment and test samples show resistances less than 5 nΩ [6]. A wire is co-wound with the conductor for quench detection purposes to cancel the inductive voltage during ramping.…”

First Hybrid Magnet for Neutron Scattering at Helmholtz-Zentrum Berlin

“…Comparable to conductor development a qualification of components like joints and procedures like coil winding was performed prior to the start of coil winding [14], [15]. A structural analysis for the three cases normal operation, quench and fault of resistive insert coil verified that the conductor stress levels stay well below the limits [16].…”

DC Resistance Performance of the Low-Resistance <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex-math></inline-formula> Joints for the CHMFL Hybrid Magnet

“…Any handling of the Nb 3 Sn conductor after heat treatment has the risk of degrading the J C performance of the conductor. Therefore, machining of the joints should be avoided after the superconducting coils are heat-treated [6]- [9]. The superconducting outsert of the 40-T hybrid magnet will be operated in the dc state, the joint will be cooled by 4.5-K supercritical helium with 1 g/s, and the temperature rise come from the joint will be controlled to be lower than 0.2 K. Hence, each joint's dc resistance will be crucial to the performance of the outsert and should be lower than 3 nΩ to meet the cryogenic cooling requirements [5].…”