Quench and self-protecting behaviour of an intra-layer no-insulation (LNI) REBCO coil at 31.4 T

Abstract

This paper presents experimental results on a quench of an intra-layer no-insulation (LNI) (RE: rare earth)Ba2Cu3O7−δ (REBCO) coil in a 31.4 T central magnetic field and simulated results on the quench. We have been designing a persistent-mode 1.3 GHz (30.5 T) nuclear magnetic resonance (NMR) magnet with a layer-wound REBCO inner coil. Protection of the REBCO coil from quench is a significant issue and the coil employs the LNI method to obtain self-protecting characteristics. We conducted high-field generation and quench experiments on an LNI-REBCO coil connected to an insulated Bi2Sr2Ca2Cu3O x (Bi-2223) coil under a background magnetic field of 17.2 T as a model of the 1.3 GHz NMR magnet. The coils successfully generated a central magnetic field of 31.4 T. Although the LNI-REBCO coil quenched at 31.4 T, this quench did not cause any degradation to the coil. A numerical simulation showed the current distribution during the quench was non-uniform and changed rapidly over time due to current bypassing through copper sheets between layers, resulting in faster quench propagation than in an insulated REBCO coil. During the quench propagation, the peak temperature (T peak) and the peak hoop stress BzJR (σθ, peak) were calculated to be 330 K and 718 MPa, respectively. These are below critical values that cause degradation. The simulation also showed that the high electrical contact resistivity (ρ ct) of 10 000 µΩ cm2, between REBCO conductors and copper sheets in the LNI-REBCO coil winding, played an important role in protection. When ρ ct was as low as 70 µΩ cm2, the quench propagation became too fast and large additional currents were induced, resulting in an extremely high σθ, peak of 1398 MPa, while the T peak was as low as 75 K. In short, the high ρ ct in the present coil caused a high T peak, but succeeded in suppressing σθ, peak and protecting the coil from the quench.

Ramping loss and mechanical response in a no-insulation high-temperature superconducting layer-wound coil and intra-layers no-insulation coil

“…Specifically, a polyimide sheet and a copper sheet are both inserted between different layers of the layer-wound coil. The experimental results indicate that not only can LNI coil reduce the magnetic field delay time, but also has high thermal stability [22].…”

Advances in second-generation high-temperature superconducting tapes and their applications in high-field magnets

“…In 2020, subsequently, the all-superconducting magnets of the IEECAS successfully reached the world record of a 32.35 T DC magnetic field. The magnet consists of a 15 T low-temperature superconductor outer coil and two high-temperature superconductor no-insulation insert coils using a conductor tape coated with REBCO, as shown in Figure 18 [133] . This is the highest field of all-superconducting magnets that have been achieved, which reflects the superiority of 2G-HTS tapes in manufacturing high-field magnets.…”

“…Figure 18. Design and construction of REBCO insert coil [133] © 2020 IOP Publishing Ltd. Printed in the UK.…”

“…Figure19. Test of REBCO insert under 15 T background magnetic field at 4.2 K[133] © 2020 IOP Publishing Ltd. Printed in the UK.…”

Effects of Wax Impregnation on Contact Resistivity Between REBCO Tapes

“…Paraffin (wax) impregnation is a process that can improve a REBCO coil's mechanical stability and has been used for insulated [8] and the layer-no-insulation [9] REBCO coils. It is conceivable that the impregnation with wax, an insulator, may have impact on the contact resistivity of a NI coil.…”