Accelerator quality HTS dipole magnet demonstrator design

Margarita Synanidi — Tue, 25 Nov 2014 10:54:57 +0000

Accelerator quality HTS dipole magnet demonstrator design
by Agnes Szeberenyi (CERN), Glyn Kirby (CERN)

Figure 1: Aligned block development HTS magnets, (bottom right) Feather-M0 quench detection development coil, (top left) Feather-M2 the EuCARD-2 five Tesla standalone approaching accelerator field quality insert magnet. Image credit: CERN

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 Future Magnets activity is a collaborative push to take HTS materials into an accelerator quality demonstrator magnet. A new coil layout concept, named aligned block was developed which can result in 2.3 times less conductor that leads to more cost efficiency than with the conventional Cosine Theta design using the same conductor.

The collaboration between CEA-CERN-KIT-TUT-INFN-LNBL aims to develop a High Temperature Superconductor (HTS) accelerator quality magnet demonstrator, capable of producing a 5 T central magnetic field in standalone configuration. Both REBCO and BSCCO conductors are being considered. The BSCCO design is part of the US-BSCCO programme based on Canted Cosine-Theta (CCT) geometry. The European collaboration is focusing on REBCO coated conductors, based on aligned block and cosine-theta.

At CERN scientists are developing the align block concept, named Feather-M0/2 (FeaTHeR - Five Tesla HTS Research, see Figure 1). Feather-M0 is used to develop coil winding and quench detection, while Feather-M2 will produce 5 Tesla standalone and between 17 and 20 Tesla, when inserted into the 100 mm aperture of Fresca-2 high field out-sert magnet. The main objective with the aligned block design is to maintain a close alignment of the magnetic field with the cable throughout the entire coil assembly. This layout makes optimal use of the anisotropy of the REBCO coated conductor (Figure 2). The design, although in its initial phase, addresses most issues related to the use of Roebel cable for a dipole cable. In a second step it is foreseen to approach a 17 T central field when inserted in a 13T high field magnet. Model coils are under construction, cables and magnet designs are progressing. Models will test dynamic field quality and confirm if it is possible to detect and protect the REBCO high current density present in the aligned Roebel cable design.

Figure 2:In the layouts the magnetic field angle is highest at the edges of the cable causing a large variation of the critical current over its width. Image credit: CERN

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issue 12

A step towards Next Generation Magnets

Margarita Synanidi — Thu, 20 Nov 2014 16:20:30 +0000

A step towards Next Generation Magnets
by Luca Bottura (CERN)

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.

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Accelerator quality HTS dipole magnet demonstrator design

A step towards Next Generation Magnets