Stress Concentration At the Joints of a Stacked NI REBCO Magnet During Quench Transient

No-insulation (NI) REBCO magnets have demon strated strong potential for generating ultra-high magnetic fields. However, many high-field NI magnets have experienced quench induced mechanical degradation, including the outer joints connecting adjacent double pancake (DP) coils. This study investigates the mechanical stress that develops at these joints during a quench, using the 45.5 T Little Big Coil 3 (LBC3) as a reference. Azimuthal currents were reconstructed from the measured voltage data using an optimization method based on evolutionary strategy. These time-dependent current profiles were then used to compute Lorentz-force-induced stress in a 2D axisymmetric finite element analysis (FEA) model. Results show that inductive coupling during the quench leads to azimuthal current imbalance between adjacent pancake coils, causing bending and high compressive stress at the outer joints. T…