The Effect of a Ferromagnetic Medium on the Field of YBCO Trapped Field Magnets

Trapped field magnets (TFMs) are characterized by the maximum field they can retain when they are activated in air (~vacuum). In some applications however, TFMs are partially embedded in a ferromagnetic medium. We consider, experimentally and theoretically, some simple geometries involving contact between TFMs and ferromagnetic media. We find: an increase in maximum TFM field exceeding a factor of 2.53; a change in field profile from the well-known conical TFM field to a uniform field in the ferromagnetic material; and fields produced by present day TFMs capable of saturating Hyperco-50 alloy. The observed flux creep rate of the TFM field was found to be the same in air and in contact with ferromagnetic material.