Persistent Current-induced Harmonics (may be a problem in Nb3Sn magnets, if done nothing)
Nb3Sn superconductor, with the technology under use now, is expected to generate persistent current-induced harmonics which are a factor of 10-100 worse than those measured in Nb-Ti magnets.
In addition, a snap-back problem is observed when the acceleration starts (ramp-up) after injection at steady state (constant field).
Measured sextupole harmonic in a Nb-Ti magnet
Measured sextupole harmonic in a Nb3Sn magnet
The iron dominated aperture in a common coil magnet system overcomes the major problem associated with magnets using Nb3Sn superconductor.