  The iron-based superconductor (IBS) single pancake coil (SPC) with 30 mm
inner diameter was firstly fabricated and tested under 24 T background field.
This SPC was successfully made using the 7-filamentary Ba1-xKxFe2As2 (Ba122)
tape by wind-and-react method. This IBS coil show the highest Ic value at
magnetic field reported so far. For example, the transport critical current of
this Ba122 SPC achieved 35 A at 4.2 K and 10 T, which is about half of that of
short sample. This indicates that the non-insulation winding process together
with the stainless-steel tape is suitable to the iron-based superconductor.
Even more encouraging is the fact that the Ic of this SPC is still as high as
26 A under 24 T background field, which is still about 40% of that at zero
external magnetic field. These results clearly demonstrate that the iron-based
superconductors are very promising for high-field magnet applications.

Superconductivity