Concept of a Cryogenic System for a Cryogen-Free 25 T Superconducting Magnet
Concept of a Cryogenic System for a Cryogen-Free 25 T Superconducting Magnet
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DOI：
10.1016/j.phpro.2015.06.095
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
S. Iwai;M. Takahashi;H. Miyazaki;T. Tosaka;K. Tasaki;S. Hanai;S. Ioka;Kazuo Watanabe;S. Awaji;H. Oguro
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文献类型：
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作者：
S. Iwai;M. Takahashi;H. Miyazaki;T. Tosaka;K. Tasaki;S. Hanai;S. Ioka;Kazuo Watanabe;S. Awaji;H. Oguro
目前正在开发一种使用ReBCO插入线圈的无致冷剂25 T超导磁体，该磁体在外部低温超导（LTS）线圈的14 T背景场中产生11.5 T。在磁场斜升期间插入线圈的AC损耗约为8.8 W，这在LTS线圈的操作温度（4 K）下难以消散。然而，由于ReBCO线圈可以在高于4K的温度下操作，ReBCO插入线圈由两个GM制冷机冷却至约10 K，LTS线圈由两个GM/JT制冷机独立冷却。两个GM制冷机通过热交换器冷却循环氦气，气体被长距离输送到位于ReBCO插入线圈上的冷级，以保护制冷机免受高磁场泄漏场的影响。增大气体流量可以减小GM制冷机第二冷级与插入盘管之间的温差。然而，与此同时，热交换器的热损失增加，并且第二冷级的温度升高。因此，通过使用流量控制器和连接到缓冲罐的旁路电路来优化气体流速，以最大限度地降低ReBCO插入线圈的工作温度。
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.