Concept of a cryogenic system for a cryogen-free 25 T superconducting magnet

Sadanori Iwai, Masahiko Takahashi, Hiroshi Miyazaki, Taizo Tosaka, Kenji Tasaki, Satoshi Hanai, Shigeru Ioka, Kazuo Watanabe, Satoshi Awaji, Hidetoshi Oguro

Research output: Contribution to journalConference articlepeer-review

3 Citations (Scopus)


A cryogen-free 25 T superconducting magnet using a ReBCO insert coil that generates 11.5 T in a 14 T background field of outer low-temperature superconducting (LTS) coils is currently under development. The AC loss of the insert coil during field ramping is approximately 8.8 W, which is difficult to dissipate at the operating temperature of the LTS coils (4 K). However, since a ReBCO coil can operate at a temperature above 4 K, the ReBCO insert coil is cooled to about 10 K by two GM cryocoolers, and the LTS coils are independently cooled by two GM/JT cryocoolers. Two GM cryocoolers cool a circulating helium gas through heat exchangers, and the gas is transported over a long distance to the cold stage located on the ReBCO insert coil, in order to protect the cryocoolers from the leakage field of high magnetic fields. The temperature difference of the 2nd cold stage of the GM cryocoolers and the insert coil can be reduced by increasing the gas flow rate. However, at the same time, the heat loss of the heat exchangers increases, and the temperature of the second cold stage is raised. Therefore, the gas flow rate is optimized to minimize the operating temperature of the ReBCO insert coil by using a flow controller and a bypass circuit connected to a buffer tank.

Original languageEnglish
Pages (from-to)326-330
Number of pages5
JournalPhysics Procedia
Publication statusPublished - 2015
Event25th International Cryogenic Engineering Conference and International Cryogenic Materials Conference, ICEC/ICMC 2014 - Enschede, Netherlands
Duration: 2014 Jul 72014 Jul 11


  • GM
  • ReBCO
  • circulating
  • cryogen-free
  • gas flow


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