Limits to High Field Magnets for Particle Accelerators

Abstract

What is the ultimate limit to high fields in superconducting magnets for particle accelerators? In this paper we review the present status of the technology, outlining the main limitations. We first analyse the needed margin for operating a magnet in an accelerator. We then review the relation between current densities, coil widths, and fields in the magnets build so far. The issue of stress and the dependence on the coil lay-out is then discussed: a careful optimization between current density and coil width can be needed to keep the forces and associated strain within acceptable limits.The main issues related to cable lay-out (strand diameter, filament size) are then discussed. We conclude by giving a hint on the requirements on a HTS conductor, and a summary of Nb-Ti and Nb 3 Sn. CERN-ATS-2012-052February 2012 Abstract 4AO-1 EDMS 1184259 1  Abstract -What is the ultimate limit to high fields in superconducting magnets for particle accelerators? In this paper we review the present status of the technology, outlining the main limitations. We first analyse the needed margin for operating a magnet in an accelerator. We then review the relation between current densities, coil widths, and fields in the magnets build so far. The issue of stress and the dependence on the coil lay-out is then discussed: a careful optimization between current density and coil width can be needed to keep the forces and associated strain within acceptable limits. The main issues related to cable lay-out (strand diameter, filament size) are then discussed. We conclude by giving a hint on the requirements on a HTS conductor, and a summary of Nb-Ti and Nb 3 Sn.

Advanced Accelerator Magnets for Upgrading the LHC

“…Probably it will run at 7.7 T, 20% less than the short sample limit of 9.7 T 2. The overall current density of the coil should be around 400 A/mm 2 , at the design field, as in all previous accelerator magnets [36]. Lower current density means a too large and expensive magnet, higher current density (if available!)…”

The EuCARD-2 Future Magnets European Collaboration for Accelerator-Quality HTS Magnets

“…Dipole field in excess of 15-16 T, the Nb3Sn limit [20], is very advantageous if the new machine will be built in the LHC tunnel (HE-LHC), see Fig. 1, given the "limited" circumference of 27 km.…”

Strategy for Superconducting Magnet Development for a Future Hadron-Hadron Circular Collider at CERN

“…These large forces require a careful stress management, as the stress limit of Nb 3 Sn magnet coils is nowadays considered to be up to 200 MPa [27]. Also the stored energy (Figure 1, right) will bear large challenges, especially to maintain a hot-spot temperature below 300 K. The copper-to-superconductor ratio has to be selected adequately in order to limit the hot-spot temperature in case of quench.…”