Park Dongkeun, Dong Fangliang, Lee Wooseung, Bascuñán Juan, Iwasa Yukikazu
Francis Bitter Magnet Laboratory (FBML)/Plasma Science and Fusion Center (PSFC), Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA.
FBML/PSFC, MIT, Cambridge, MA 02139, USA. He is now with Gwangju Center, Korea Basic Science Institute, Buk-gu, Gwangju, 611856, South Korea.
IEEE Trans Appl Supercond. 2023 Aug;33(5). doi: 10.1109/tasc.2023.3252487. Epub 2023 Mar 3.
As a preliminary work, we have completed a 12.5-mm-cold-bore high-temperature superconducting (HTS) REBCO magnet prototype and successfully operated it up to 25 T at 10 K cooled by a cryocooler only, without liquid helium. In this paper we present the first-cut design of a cryogen-free all-REBCO 23.5-T/25-mm-warm-bore magnet having a high homogeneity of <0.1 ppm over a 1-cm diameter of spherical volume for a benchtop 1-GHz microcoil NMR spectroscopy. We also investigate a shielding design to reduce a 5-gauss fringe field radius to ≤1.5 m. This benchtop magnet will incorporate all the innovative design and operation concepts validated by the prototype magnet: 1) all-HTS composition and operation at above 4.2 K; 2) no-insulation winding technique with an extra shunting that makes this high-field REBCO magnet compact, mechanically robust, and self-protecting; 3) a single coil formation that leads, compared with the traditional multi-nested high-field NMR magnet, to simpler and more affordable manufacturing processes; 4) operational temperature-controlled screening-current reduction method which reduces peak stresses within the REBCO coil and field errors; and 5) cryogenic design for conduction-cooling operation.
作为前期工作，我们已完成了一个内径为12.5毫米的冷孔高温超导（HTS）REBCO磁体原型，并仅使用低温制冷机在10 K下成功将其运行至25 T，无需液氦。在本文中，我们展示了一种无液氦的全REBCO 23.5 T/25毫米温孔磁体的初步设计，该磁体用于台式1 GHz微线圈核磁共振光谱，在直径1厘米的球形体积内具有<0.1 ppm的高均匀性。我们还研究了一种屏蔽设计，以将5高斯边缘场半径减小至≤1.5米。该台式磁体将采用原型磁体验证的所有创新设计和运行理念：1）全HTS组成并在4.2 K以上运行；2）无绝缘绕组技术及额外的分流，使该高场REBCO磁体紧凑、机械坚固且具有自我保护能力；3）单线圈结构，与传统的多层嵌套高场核磁共振磁体相比，制造工艺更简单、成本更低；4）运行温度控制下的屏蔽电流降低方法，可降低REBCO线圈内的峰值应力和场误差；5）用于传导冷却运行的低温设计。
