The current status of large-grained RE-Ba-Cu-O (RE: Y or rare earth elements) bulk superconductors with excellent superconducting properties is described. Gd-Ba-Cu-O bulk superconductors can trap a very high magnetic field even if they are melt-processed in air. Although the electromagnetic force caused by the trapped field is larger for a larger sample and may break the sample, a large sample of Gd-Ba-Cu-O 46 mm in diameter has the potential of trapped magnetic fields greater than 10 T at around 40 K. In addition, single-grained bulk superconductors as large as 150 mm can be obtained using the RE compositional gradient method. Dy-Ba-Cu-O is an ideal material for current leads because it has low thermal conductivity and high critical current density at 77 K in high magnetic fields. Eu-Ba-Cu-O has low magnetic permeability, and is therefore suitable for bulk NMR applications. Progress in machining technology has made possible various bulk superconductors with complicated shapes such as coils, leading to small and strong electromagnets by stacking several coil-shaped bulk superconductors together.
The applications of REBaCuO superconducting bulks (RE: rare earth element or Y) have been investigated recently because of the enhancement of the superconducting characteristics such as critical current density Jc and the trapped field BT. A superconducting bulk can trap higher BT of over 17 T via conventional field-cooled magnetization (FCM) and BT=5.2 T via pulsed field magnetization (PFM), which has been intensively studied because a superconducting magnet is not used. This review article summarizes the magnetizing mechanism of the superconductors, the recent activities of PFM conducted experimentally and numerically, and the practical applications of several superconducting bulk magnet devices.
In this article, the development progress of our GdBaCuO 30-kW-grade bulk HTS motor is presented. Two main features will be described here: the addition of the bulk HTS field poles using magnetic particles, and the amelioration of the condensed-neon cooling system through the addition of a gaseous helium phase. Owing to this new cooling procedure, the cooling time of the motor was reduced by more than 30% and the flux decay following the in-situ magnetization of the bulk HTS was halved. The addition of magnetic particles into the Gd-123 bulks allowed a 1.1- to 1.4-fold trapped flux density and an additional reduction of the flux decay from 7% to approximately 4% after five hours of synchronous operation under an AC field.