Speaker
Description
The goal of building economic 16 T accelerator magnets requires Nb3Sn conductors with Jc much higher than state of the art. Thus, a lot of efforts in the Nb3Sn community have been focused on improving Jc (while keeping RRR and effective subelement size deff in the acceptable range). However, a very important factor that is also critical for this application but has been overlooked is the persistent-current magnetization M, because large M leads to critical issues such as flux jumps, field errors, and large a.c. loss. Conceptual design studies for the proposed Future Circular Collider (FCC) 16 T dipoles show that the large M is a significant problem to address. One way to reduce M is to reduce deff, but this may sacrifice Jc as deff is below 30-40 micron. In this study we measured the M-H loops of RRP® and the new APC conductors up to 25 T. The results showed that the APC conductors have higher non-Cu Jc at high fields (e.g., 32-41% higher at 16 T) and simultaneously lower non-Cu Jc at low fields (e.g., 28-34% lower at 1 T) compared with the RRP®. Assuming that both have the same non-Cu Jc at 4.2 K, 16 T (e.g., 1500 A/mm2), then the non-Cu Jc and magnetization (for the same deff) of an APC conductor is only 50% or less relative to an RRP® conductor at 1 T. This is because APC strands have much flatter Jc-B curves than standard Nb3Sn due to the point pinning behavior (as a result of the nano oxide particles).
