Electromagnets are an important application of superconductivity as superconductors can provide large current density in the winding pack without any voltage drop or joule heating losses. High temperature superconducting (HTS) magnets have advantages over low temperature superconducting (LTS) magnets, particularly because HTS magnets have better stability and possibility of producing magnetic field higher than 20 T. However, protection of HTS magnets is challenging due to slow normal zone propagation (NZP). When the NZP is slow, the stored magnetic energy is dissipated at localized area where the hot spot temperature can rise significantly and can cause "burn-out" damage on the superconductor. The no-insulation (NI) HTS winding technique has been experimentally demonstrated to be a promising technology, particularly to prevent a coil from electric burn-out, and has made it possible to reach a magnetic field of 45.5 T at the magnet center. NI magnets are dry wound and this adds to the ease in construction of NI coils as difficult epoxy impregnation process or wet winding process can be eliminated. The lack of insulation makes the magnet compact due to larger engineering current density, Je. Je of up to 1580 A/mm2 has been reported in NI coils, which is significantly larger than observed in insulated counterparts. The lack of low strength insulation also makes the magnet robust. NI winding using REBCO does not require processing steps such as epoxy impregnation or heat treatment, making its construction faster and convenient. However, as seen from the evidences of mechanical damage (seen from microscopy and critical current measurement) on the 45.5 T insert coil, there is a limit to this otherwise exciting technology. This research explores, in both simulation and experiment, the post-quench behaviors of NI magnets to quantitatively understand their self-protecting mechanism. NI quench modeling is challenging due to its non-linear, extremely fast and interrelated multiphysical behavior. A lumped circuit model combined with heat transfer and solid mechanics models is used to explain electrical, thermal, and mechanical responses in detail at the magnet level. In this model, each subcoil is modeled as single inductor (L M) with variable resistances in series (Rq) and in parallel (Rc). For this purpose, some magnets that have been constructed and quenched at 4.2 K are being analyzed, which are 1) a stack of 3 double-pancake (DP) coils, 2) 14.5 T insert in 31 T resistive magnet, 3) 2 DP insert in 31 T resistive magnet, 4) 7 T standalone magnet, 5) 26 T standalone magnet, 6) 13 T HTS insert in 7 T background LTS magnet. The lessons learned from analysis of these magnets are presented in this work. The quench modeling allows us to look at temperature and stress in the magnet that are difficult to measure, but are important to make sure damages due to burn-out or overstraining do not occur during operation. With the lessons learned, this approach can now be used for future design of high field magnets to make sure mechanical damage during the magnet quench is prevented.
