Quench Phenomena in a Conduction-cooled Fast-ramping High Temperature Superconducting (HTS) Magnet

A conduction-cooled HTS magnet was tested to produce an AC magnetic field up to 4 T for an adiabatic demagnetization refrigerator (ADR). Quench detection was conducted by measuring the voltages in the conductor, and the protection system was constructed with an external dump resistor. The magnet, which is equipped with extensive copper thermal drains, was conduction-cooled by a two-stage Gifford-McMahon cryocooler to approximately 6 K. The magnet succeeded to stably generate an alternating magnetic field between 0 and 3.5 T at a ramp rate of 229 mT/s without any pre-quench signs; however, in the case of a maximum 4 T experiment, a quench occurred, and the magnet was permanently damaged. The quench location was identified as the place where the highest perpendicular field from the magnet was generated. It is speculated that the already-formed normal zone before quench grows very fast during the dump process, and part of the magnetic energy is dissipated in this normal zone, causing the excessive temperature rise of the conductor. The detailed experimental results are presented and discussed.