New cryocooler-cooled superconducting magnet: A 13.5 T high-field split-pair coil magnet for neutron scattering

A new high-field superconducting magnet of the cryogen-free type has been developed. The superconducting coil of this system is directly cooled down by three 4 K-GM cryocoolers. The magnet consists of a split-pair of (Nb,Ti)3Sn inner coils and NbTi outer ones; and its outer diameter is 545 mm and the height is 352 mm. The gap for the beam path is 18 mm at the horizontal level. These upper and lower coils are supported by five Al alloy rings and an Al alloy plate of 90o in angle. The total thickness of the Al alloys in the beam-path is 65.2 mm, and the transmission of about 60% for 13.7 meV neutrons is obtained. The bore at room temperature is 51 mm in diameter. In this bore a sample cooling-system of a 4 K-cryocooler or a cryogen-free dilution refrigerator is inserted. The size of the standard sample cell is 35 mm in diameter. In this sample space nonmagnetic high pressure cells up to 4 GPa can be set in. With these apparatus experiments under multiple extreme conditions are achieved. Some difficulties encountered during this development are briefly described. Now the maximum field in ordinary use of 13.5 T is stably obtained