Bulk superconducting magnets with fields beyond 14 T

Abstract

Bulk YBa 2Cu 3O 7− x (YBCO) material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texturing process. A maximum trapped field, B 0, up to 1.1 T at 77 K was obtained on the top of a single YBCO disk 25 mm in diameter by chemical doping of Zn on Cu plane sites increasing up to 9 T at 43 K due to the increasing critical current density at lower temperatures. At temperatures around 50 K, the trapped field is limited by the mechanical properties and cracking of the material which is exposed to considerable tensile stresses due to Lorentz forces acting during the magnetization procedure on the superconductor. Very high trapped fields up to 14.4 T were achieved at 22 K in the gap betweeen two YBCO disks by the addition of silver improving the fracture toughness of the material and by using a bandage made of steel. This is the highest trapped field achieved so far in a bulk superconductor. On the top of a single YBCO disk, a maximum trapped field of 11.5 T was obtained at 17 K. In order to use superconducting YBCO permanent magnets in superconducting magnetic bearings, an effective method for magnetizing the superconductor is required. Results of magnetizing YBCO samples by applying pulsed magnetic fields will be presented.