Modeling Current-Field Instabilities in High Performance Nb₃ Sn Strands in Moderate Field

High Performance internal-Sn-type Nb3Sn strands are only marginally stable. This has significant consequences for strand measurement at higher fields (12 T), and leads to magnetic flux jumping at lower fields (0-1 T). However, the most troublesome regimes of instability from a magnet maker's point of view are moderate fields where current transport and external magnetic fields interact to create an instability not evident from magnetization at current levels well below that predicted by higher field results. These effects can be described in terms of adiabatic and dynamic stability, using a model first developed by Wilson. Modifications are presented for a multifilamentary strand, with HEP-relevant values of deff, RRR, strand diameter, Jc, and local thermal environment. Model predictions are compared to experimental strand results to bring out the relative functional dependence of stability on RRR and deff.