Liquid helium-free 15 T superconducting magnet at 4 K

We have successfully demonstrated a 15.1 T liquid helium-free superconducti ng magnet with a room-temperature bore of 52 mm using a Nb3Sn/NbTi hybrid c oil, Bi2223 current leads and two Gifford-McMahon cryocoolers. The magnet h as 830 mm outside diameter, 1221 mm height and 720 kg weight. The magnet wa s cooled to 3.6 K in 114 h. A central magnetic field of 15.1 T was achieved in 38 min. The temperature of the coil increased to 5.7 K due to ac losses during the excitation, but it decreased to 4.0 K before reaching 15.1 T. T he temperature of the coil remained at a constant value of 3.8 K over the 2 4 h of operation. The demonstration indicated the usefulness of a liquid he lium-free superconducting magnet to generate high magnetic fields up to 15 T.