Seminar By Jun Lu, MS&T, National MagLab
Title: 'To be or not to be' — insulation for HTS magnets
Abstract: Wire insulation technology is a crucial part of magnet coil technology. It is said that most magnet coil failures are results of or related to insulation failure. High Tc superconductor (HTS) magnets have been under rapid development worldwide led by the MagLab. Evidently the insulation technology for HTS magnets needs to be developed. As it turned out, the insulation development is particularly challenging as I will explain in the talk.
It is actually possible to operate a superconducting magnet with no insulation. In fact, no insulation and partial insulation REBCO magnets are a new, promising magnet technology that has the potential to produce very efficient magnets. In principle, a superconductor has no electrical resistance and an equal electrical potential. So in steady state operation, there is no turn-to-turn voltage, as a result, no turn-to-turn short/leak current. But situation is much more complicated during a field ramp when turn-to-turn contact resistance becomes very important and needs to be managed as I will explain.
I will first present the technology of SiO2/Al2O3 insulation on co-winding stainless steel tape for the REBCO insert coils of our 32 T all-superconducting magnet. It will be followed by the story of Bi-2212 wire insulation with TiO2-based ceramic coating, and the remaining challenges of this technology. Finally, I will present our recent works on partial insulation (resistive turn-to-turn contacts) for REBCO coils.