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

This paper presents experimental results on a quench of an intra-layer no-insulation (LNI) (RE: rare earth)Ba2Cu3O7-delta (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 B(z)JR (sigma(theta,) (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 (rho (ct)) of 10 000 mu omega cm(2), between REBCO conductors and copper sheets in the LNI-REBCO coil winding, played an important role in protection. When rho (ct) was as low as 70 mu omega cm(2), the quench propagation became too fast and large additional currents were induced, resulting in an extremely high sigma(theta,) (peak) of 1398 MPa, while the T (peak) was as low as 75 K. In short, the high rho (ct) in the present coil caused a high T (peak), but succeeded in suppressing sigma(theta,) (peak) and protecting the coil from the quench.

Automated summary

This paper presents experimental and simulated results on the quench of an intra-layer no-insulation (RE: rare earth)Ba2Cu3O7-delta (REBCO) coil in a 31.4 T central magnetic field. The study shows that high electrical contact resistivity plays an important role in protecting the coil during the quench process.