Performance of a cryogen-free 30 T-class hybrid magnet

The world's first cryogen-free hybrid magnet, which was developed at the High Field Laboratory for Superconducting Materials in order to realize an easy-operational magnet system with no use of liquid helium and nitrogen, has achieved 22.7 T in a 52 mm room temperature bore. After this success, we started to construct a new cryogen-free 30 T-class hybrid magnet, consisting of an outer wide-bore cryogen-free 11 T superconducting magnet and an inner water-cooled 19 T resistive magnet. Up to now, the NbTi outer section coil and the Nb₃Sn inner one of a wide-bore cryogen-free superconducting magnet has generated individual central fields of 5.3 T at 350 A and 5.8 T at 303 A, respectively in a 360 mm room temperature bore. The wide-bore cryogen-free superconducting magnet was energized up to 9.5 T as a total background field. In hybrid magnet mode the system was operated up to an 8.5 T background field form the cryogen-free supercon-ducting magnet, because a cooling problem was encountered with the innermost coil bobbin during ramping the Bitter magnet. As a result, the cryogen-free hybrid magnet generated 27.5 T in a 32 mm room temperature bore.