Field enhancement of a 12.5-T magnet using holmium poles

Unlike conventional ferromagnetic materials such as iron and Supermendur, which produce saturation magnetization fields of approximately 2 T, several of the rare-earth elements (holmium, terbium, erbium, gadolinium, and dysprosium) yield saturated fields of nearly 4 T. This property makes these rare-earth metals particularly attractive as flux concentrators for use in superconducting magnets. This report concerns the use of holmium inserts to enhance the peak useful field of the nominally 12.5-T, 5-cm-bore tape magnet manufactured by the Intermagnetics General Corporation (IGC). Nonlinear magnetostatic analysis indicates that this field increases to nearly 16 T with the rare-earth poles inserted within the bore on both sides of the coil's split-plane radial access gap. This paper focuses on computer modeling methods and experimental results.