Tanaka Hiromi, Li Yi, Choi Yoonhyuck, Park Dongkeun, Lee Wooseung, Tanaka Hideki, Bascuñàn Juan, Iwasa Yukikazu
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA and also with National Institute of Technology, Yonago College, Tottori, 6838502 Japan.
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA. They are now with University of Houston, Houston, Texas 77204, USA, and Facility for Rare Isotope Beams, Michigan State University, 640 South Shaw Lane, East Lansing, MI 48824, USA.
IEEE Trans Appl Supercond. 2021 Aug;31(5). doi: 10.1109/tasc.2021.3064517. Epub 2021 Mar 8.
We suggested an MgB joint process with its own heat-treatment schedule to apply it for our 1.5-T MgB "finger" MRI magnet. In fabricating the MgB magnet, the optimal heat-treatment schedule to attain a reproducible and high critical current is different in a joint and a coil. To solve this problem, we introduced an additional heating system, which is composed of a cartridge heater and a thermocouple connected with a copper block, into a box-type furnace. Then, we carried out heat-treatments with exclusively increasing the joint-part temperature above the Mg melting point of 645 °C-the joint was actually heated up to 700 °C. We evaluated a critical current and a crystal structure of the obtained MgB joint. From experimental results, we found that the joint heated with the own heat-treatment schedule, which is 700 °C for 1 h + 600 °C for 11 h, showed a good of over 450 A at 15K under self-field. The joint resistance was estimated by the coil operation for 18 days, and it was expected to be less than 10 Ω.
我们提出了一种具有自身热处理方案的MgB接头工艺，以将其应用于我们的1.5-T MgB“指状”MRI磁体。在制造MgB磁体时，在接头和线圈中，实现可重复且高临界电流的最佳热处理方案是不同的。为了解决这个问题，我们在箱式炉中引入了一个由加热棒和与铜块相连的热电偶组成的额外加热系统。然后，我们进行了热处理，专门将接头部分的温度升高到高于镁熔点645°C的温度——接头实际加热到700°C。我们评估了所得MgB接头的临界电流和晶体结构。从实验结果来看，我们发现按照自身热处理方案（700°C保温1小时 + 600°C保温11小时）加热的接头在自场下15K时显示出超过450 A的良好临界电流。通过线圈运行18天对接头电阻进行了估算，预计其小于10Ω。
