Mini-RT装置用高温超伝導磁気浮上コイルの冷却・励磁試験

Abstract

A magnetically levitated superconducting coil device, Mini-RT, has been constructed using a high temperature superconductor (HTS) for the purpose of examining a new magnetic confinement scheme of high-beta non-neutral plasmas. The floating coil and persistent current switch (PCS) are wound with silver-sheathed Bi-2223 tapes, and they are operated in the temperature range of 20-40 K. After the basic properties of the main coil and HTS-PCS were examined in a liquid helium cryostat, the coil was installed into the vacuum chamber of the Mini-RT device. The HTS floating coil was then cooled by helium gas using GM cryo-coolers equipped with detachable transfer tubes. The excitation tests of the coil were carried out by supplying current from an external DC power supply through the detachable current feeder terminals as the HTS-PCS was turned off. The nominal operation condition was examined by overcoming many difficulties and the persistent current mode was tried by turning on the HTS-PCS. The decay time-constant was evaluated by maintaining the coil temperature for up to four days and the results were compared with calculations. The first magnetic levitation was also examined.