A step towards Next Generation Magnets
A Roebel cable prototype, inserted in a sample holder and ready for test at low temperature and high field in the CERN FRESCA test facility. Image credit: J. Fleiter, CERN
The Future Magnets, Work Package 10 of EuCARD-2 is exploring the use of High Temperature Superconductors (HTS) materials in future accelerator magnets: YBCO and BSCCO. Both YBCO and BSCCO were found to have not only a high critical temperature, but also a very high critical field, exceeding 100 T. This is what makes them especially interesting for high field accelerator magnet applications.
Following an evaluation performed by the EuCARD2 WP10 team, and the associated laboratories in the US and Japan, it was decided that the European program would focus on YBCO tapes, assembled in Roebel bars or, as an option, stacked tapes. YBCO is a material produced by one of the industrial partners of EuCARD-2 (Bruker HTS), and has potential for use both in very high field applications beyond the scope of WP10, such as Nuclear Magnetic Resonance magnets, as well as power applications such as Fault Current Limiters or high current power transmission cables. Accelerator magnets require high current, and the Roebel bar is a way devised by KIT to assemble multiple YBCO tapes in a high current transposed conductor. Samples of such conductors were already tested at CERN at cryogenic conditions (4.2 K) and intense field (10 T), showing the desired high current carrying capability. The EuCARD2 WP10 will produce samples of YBCO Roebel bars in the coming months.
As for the alternate material, EuCARD2 makes a significant contribution by providing the precursor powders necessary for the production of the BSCCO-2212 superconducting wire.
The question for the coil cross section is yet open for both Roebel bars and Rutherford cables; the magnet geometry for making the optimal use of the current carrying capacity of the superconductor, and respecting the engineering limits of the materials, is not necessarily the same.
