Prospects for the use of high temperature superconductors in high field accelerator magnets

Several future accelerators will require magnets to operate above 10 T (for example the proposed Muon and Hadron colliders). In this new domain of accelerator magnets, the pre-eminence of Nb-Ti falls away. In the time frame of new accelerator construction (10-20 years), there are strong opportunities to bring on new classes of superconductor (advanced A15, HTS), provided that serious, focused efforts start soon. Of the primary HTS superconductors, Bi₂Sr₂CaCu₂O_x, (Bi,Pb)₂ Sr₂Ca₂Cu₃O_x, and YBa ₂Cu₃O₇, the most promising for near-term high field magnet application is Bi₂Sr₂CaCu₂O_x (Bi-2212). However, HTS conductors are still at an early stage of development and continued improvement over the next ten years could make other HTS superconductors available for accelerator application, Bi-2212 appears to have the highest potential today, because it can be made in round wire form with reasonably high J_c values, thus permitting access to the cabling technology developed for LTS materials. Bi-2223 and YBCO are both presently limited to wide-tape designs, for which cabling is a significant challenge. Development of less aspected conductor designs might permit YBCO coated conductors to drive out 2212 as the present conductor of choice. An alternative approach is to design magnets around the use of aspected conductor forms and anisotropic properties in order to make the most of the unique properties of HTS superconductors