Abstract
The no-insulation, or more precisely, controlled-resistance coil winding method, nowadays being exclusively used for high-temperature superconducting solenoids, has proven its effectiveness for improving quench protection. When considering low-temperature superconductor magnet technology, which is mostly focused on stability and training issues, controlled-resistance insulation windings are directly addressing these aspects as well. Fully soldered coil windings of non-insulated turns can also show superior mechanical properties and feature simplified manufacturing when compared to epoxy impregnated coil windings and are of high practical interest for quasi-stationary magnets provided the related charging time constant can be controlled and kept low enough. For demonstrating the principle feasibility two demonstrator coils were developed using NbTi/Cu wire with CuNi cladding of 1 mm diameter. The wire performance is reported including critical current and n-values at 4.2 K and background magnetic fields from 0 to 9 T, as well as effective transverse resistivity at room temperature and 77 K. Two solenoids with fully soldered windings comprising one layer on a 50 mm bore and three layers on a 100 mm bore, respectively, were manufactured and tested in liquid helium. Their performance is directly compared to data obtained on short wire samples. The drastically enhanced stability of the coils against thermal disturbances allows to avoid any training and enables to operate the coils up, or even slightly beyond, the short-sample critical current, resulting in generated magnetic fields of 2.2 and 3.8 T and time constants of 5 and 55 s, respectively. When initiating a quench deliberately by excessive heating or spontaneously at their limiting currents, the coils entirely switch to the normal state almost instantly, thus requiring no quench protection system. Design, manufacturing and test experiences with the two super stable coils are reported and their use and design constraints for certain applications discussed.
Highlights
Superconducting magnet technology has been successfully employed in the construction of electromagnets with high stored energy, up to the GJ range [1]
Such magnets are operated at relatively low current density J, some tens of A/mm2, using large amount of stabilizer in the conductor, which is mostly dictated by quench protection requirements [2], and they would even follow E ∼ J−6 scaling if designed as cryostable [3]
Advanced detector magnets are often aimed at achieving minimal thickness of coil windings in order to ensure maximum radiation transparency, with applications ranging from particle physics [4] to magnetic spectrometers in space [5]
Summary
Superconducting magnet technology has been successfully employed in the construction of electromagnets with high stored energy, up to the GJ range [1] Such magnets are operated at relatively low current density J, some tens of A/mm, using large amount of stabilizer in the conductor, which is mostly dictated by quench protection requirements [2], and they would even follow E ∼ J−6 scaling if designed as cryostable [3]. An alternative solution to restrain the characteristic coil charging time constant τ in fully soldered NbTi/Cu wire based windings is investigated It is based on using a highly resistive CuNi cladding surrounding the standard NbTi/Cu wire, a technique that may be applied in ReBCO coils as well. 1.0 mm 17 mm 1.7 ± 0.1 336 ≈ 30 μm ≈ 100 μm Essential design constraints and potential applications are discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
