A superconducting magnet generating fields over 18 T

A superconducting magnet has been constructed and succeeded in generating a field of 18.1 T by the operation at 4.2 K without any quenching. This field is the new highest record generated by a superconducting magnet so far. The maximum stored energy of the magnet is about 6 MJ. The magnet consists of an outer magnet (I) with a 455 mm bore, an outer magnet (II) with a 180 mm clear bore and an inner magnet with a 30 mm clear bore. The conductor used in the outer magnet (I) is a monolithic multifilamentary Nb-Ti and that used in the outer magnet (II) is a monolithic multifilamentary (Nb,Ti)3Sn. The outer magnet (I) and (II) are electrically connected in series to complete an outer magnet which is excited up to 14.2 T at 4.2 K. The inner magnet is an assembly of pancakes made of surface diffusion processed V3Ga tapes and insitu processed V3Ga tapes, and excited by another DC power supply up to an incremental field of 3.9 T at 4.2 K in the back-up field of the outer magnet. The high stability of the outer magnet makes the operation of duplex superconducting magnet system convenient and safe. We are planning to generate fields above 20 T by the operation of this magnet system at 1.8 K.