Magnetic field decay in model SSC dipoles

The authors have observed that some of the model SSC dipoles have long-time-constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 Tesla for one to three hours, and changes in the magnetic field were observed. One explanation for the observed field decay is time-dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep as mechanisms for the observed field decay is discussed.<
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