Operation of 17.5 T superconducting magnet system in the last 8 years

A 17.5 T hybrid superconducting magnet with an outer Nb3Sn section and an inner V3Ga section was installed at National Research Institute for Metals (Japan) at the beginning of 1976. Since then the magnet system has been successfully operated about 60 times without any trouble. The magnet still generates the world-highest field in the superconducting state. Ordinarily, it is cooled from room temperature down to about 15 K using two helium refrigerators with a total refrigeration power of 750 W at 20 K. For one day operation, about 120 liters of liquid is transfered into the cryostat. It requires about 2 hours to induce the magnetic field from 0 to 17.5 T. The liquid helium evaporation rate is about 4.5 liters/hr when the magnet is in full operation. To suppress the instability due to the tape movement, it was necessary to refasten tie-rods between the upper and lower flanges of the magnet during the first few years after the installation. The magnet has been effectively used to measure the critical current of newly developed high-field superconductors.