Development of Large-Bore Superconducting Magnet With Zero-Vapor Liquid Helium

A large bore NbTi superconducting magnet with liquid helium bath cooling has been developed for a micro-sized superconducting magnetic energy storage (SMES). The superconducting magnet has the clear bore of 480 mm, outer diameter of 550 mm and height of 500 mm. The magnet system is cooled in a compact cryostat with two GM cryocoolers. One of the cryocoolers is used to cool the thermal shielding. Another is used to re-condense the helium evaporation. A pair of high temperature superconducting current leads is used to reduce heat load to the cryostat. The operating current of the SMES system is rated at 325 A. Maximum energy storage is evaluated as 1.0 MJ at the rated operating current. Test results show that the stored energy can be dumped at the power of 7 kW to a dummy resistor load. This superconducting magnet system can be demonstrated as an Uninterruptible Power Supply (UPS). The superconducting magnet and the cryogenic system are described in this paper.