Kim Youngjae, Hahn Seungyong, Voccio John, Song Jungbin, Bascuñán Juan, Iwasa Yukikazu
Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
IEEE Trans Appl Supercond. 2015 Jun;25(3). doi: 10.1109/tasc.2014.2365738. Epub 2014 Nov 7.
This paper deals with the mechanical strain issue in a high-temperature superconducting (HTS) insert for a GHz-class (> 23.5 T) LTS/HTS NMR magnet. We present results, experimental and analytical, of hoop strains in a double-pancake (DP) test coil, wound with 6-mm wide YBCO coated conductor (CC) and equipped with strain gauges at their innermost and outermost turns. To keep the YBCO CC to within a 95% Ic retention, the conductor tensile strain must be limited to 0.6%. To satisfy this strain limit in our test DP coil, we wrapped 0.08-mm thick, 6-mm wide stainless steel strip over its outermost turn of an 4.8-mm overband radial build deemed sufficient by our stress analysis based on force equilibrium and generalized Hooke's law with plane stress approximation. A control test DP coil, actually the same test DP coil, without overbanding, was run under the same experimental condition. In each case the test DP coil was energized up to 350 A at 4.2 K in a background field of 4 T. We report the experiment and analysis, with discussion on the merit of overbanding as a means to limit hoop strain in high-field HTS inserts.
本文探讨了用于千兆赫兹级（>23.5 T）低温超导/高温超导核磁共振磁体的高温超导（HTS）插入件中的机械应变问题。我们给出了双饼式（DP）测试线圈中环向应变的实验和分析结果，该测试线圈由6毫米宽的钇钡铜氧涂层导体（CC）缠绕而成，并在其最内圈和最外圈安装了应变片。为使钇钡铜氧涂层导体的临界电流保持在95%以内，导体的拉伸应变必须限制在0.6%以内。为了在我们的测试双饼式线圈中满足这一应变限制，我们根据力平衡和平面应力近似下的广义胡克定律进行应力分析，认为在其外径为4.8毫米的径向叠绕结构的最外圈缠绕0.08毫米厚、6毫米宽的不锈钢带就足够了。一个未进行叠绕的对照测试双饼式线圈，实际上就是同一个测试双饼式线圈，在相同的实验条件下运行。在每种情况下，测试双饼式线圈在4 T的背景场中于4.2 K下通以高达350 A的电流。我们报告了实验和分析情况，并讨论了叠绕作为限制高场高温超导插入件中环向应变的一种手段的优点。
