Quench modeling of a short-period Nb 3 Sn undulator magnet

Long Nb 3 Sn superconducting undulators (SCUs) can exhibit section-dependent quench voltage evolution that current decay data alone cannot capture while the resulting internal voltage directly governs insulation design. We present an in-house COMSOL Multiphysics two-dimensional (2D) quench-analysis model that couples electromagnetic, thermal and circuit physics to resolve the sectional and internal voltage evolution of short-period Nb 3 Sn SCUs. The 2D formulation is adopted as a geometric simplification that reduces computational cost while preserving the coupled dynamics; longitudinal circuit behavior enters through scaling lengths for inductance and resistance calibrated on the short prototype. Using independently measured critical current and residual resistivity ratio (RRR) data for the conductor, the model is benchmarked against intentional-quench tests of SMM6, a 0.1 m prototype, reproducing both the measured current decay and the sectional voltage profiles. Extended to the 0.5 m prototype IMM1, the model reproduces the measured sectional-voltage asymmetry between the magnet halves when a section-dependent RRR variation—of a magnitude consistent with the sample-to-sample scatter documented for this conductor—is included, whereas a comparable variation in the interfilament coupling parameter does not. Sectional voltage is therefore a sensitive indicator of winding non-uniformity, and internal-voltage analysis is essential to the protection and insulation design of future Nb 3 Sn undulator magnets.