Time decay measurements of the sextupole component of the magnetic field in a 4-cm aperture, 17-m-long SSC dipole magnet prototype

A systematic series of measurements of the time decay of the sextupole component of the magnetic field in a full-length SSC (Superconducting Super Collider) dipole magnet prototype was carried out in order to characterize the mechanisms involved. At least two mechanisms have been isolated. The first is a slow logarithmic decay which is independent of the excitation history of the magnet. This component is stopped by a decrease of the magnet temperature and is identified with flux creep. The second component, which is not yet fully understood, only appears when the magnet is pre-cycled to a high level of current, and cannot be stopped by decreasing the magnet temperature. The first component is attributed to flux creep in the superconductor. The authors are currently developing a model of demagnetization caused by shifting/transport currents in the superconducting cables that could account for the secondary component.<>