Persistent-Current Magnetization Effects in High-Field Superconducting Accelerator Magnets

Magnetic field changes in superconducting filaments are shielded by the so-called persistent currents. These currents produce field errors, which are particularly important at low energy level, where the effect is stronger compared to the field generated by the transport current. For the next generation of particle accelerators, magnetic fields higher than 10 T are needed, requiring the use of Nb3Sn as superconductor. Due to the larger filament size (typically ten times larger than in the Nb-Ti Large Hadron Collider dipoles) and higher current density, strand magnetization effects shall be carefully studied. This paper presents an analysis on the expected field errors due to persistent currents in a 16-T dipole magnet. We briefly discuss the method and compare with experimental results on the 11-T Nb3Sn dipole for the Hi-Luminosity upgrade. The model is then used to predict the persistent-current effects for different coil layouts and strand characteristics in a 16-T dipole.