Limits of NbTi and Nb3Sn, and Development of W&R Bi–2212 High Field Accelerator Magnets

NbTi accelerator dipoles are limited to magnetic fields (H) of about 10 T, due to an intrinsic upper critical field (H_c2) limitation of 14 T. To surpass this restriction, prototype Nb₃Sn magnets are being developed which have reached 16 T. We show that Nb₃Sn dipole technology is practically limited to 17 to 18 T due to insufficient high field pinning, and intrinsically to 20 to 22 T due to H_c2 limitations. Therefore, to obtain magnetic fields approaching 20 T and higher, a material is required with a higher H_c2 and sufficient high field pinning capacity. A realistic candidate for this purpose is Bi-2212, which is available in round wires and sufficient lengths for the fabrication of coils based on Rutherford-type cables. We initiated a program to develop the required technology to construct accelerator magnets from ´wind-and-react´ (W&R) Bi-2212 coils. We outline the complications that arise through the use of Bi-2212, describe the development paths to address these issues, and conclude with the design of W&R Bi-2212 sub-scale magnets.