A Field-Shaking System to Eliminate the Screening Current-Induced Field in the 800-MHz HTS Insert of the MIT 1.3-GHz LTS/HTS NMR Magnet: A Small-Model Study

In this paper, we present results, experimental and analytical, of a small-model study, from which we plan to develop and ap-ply a full-scale field-shaking system to minimize or even elim-inate the screening current-induced field (SCF) in the 800-MHz HTS Insert (H800) of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction—the H800 is composed of 3 nested coils, each a stack of no-insulation (NI) REBCO dou-ble-pancakes. In 1.3G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we use two NI REBCO double-pancakes, one from 2 coils (HCoil2 and HCoil3) of the 3 H800 coils, and place them in the bore of a 5-T/300-mm room-temperature bore external magnet. The external magnet is used not only to induce SCF in the double-pancakes but also elimi-nate it by the field-shaking. For each run, we induce SCF in the double-pancake at an axial location where the external radial field Br > 0, then for the field-shaking, move to another location where the external axial field Bz >> BR. To examine if other SCF eliminating techniques, e.g., the current-sweep-reversal (CSR) method, is applicable to H800 even when L500 and H800 are series-connected, we perform similar sequences of test for other combinations of the double-pancake axial locations. In this paper, we report 77-K experimental results, develop an analy-sis that satisfactorily explains the results, and apply the analy-sis to design a field-shaking system for 1.3G at full operation.

本论文报道了一项小尺度模型研究的实验与分析结果，基于该研究我们计划开发并应用一套全尺寸场抖动系统，以尽可能抑制甚至消除正在建造中的MIT 1.3GHz低温超导（Low Temperature Superconductor, LTS）/高温超导（High Temperature Superconductor, HTS）核磁共振（Nuclear Magnetic Resonance, NMR）磁体（1.3G）的800MHz高温超导插入磁体（H800）内的屏蔽电流感应场（Screening Current-induced Field, SCF）。H800由3个嵌套线圈组成，每个线圈均为无绝缘（No-insulation, NI）稀土钡铜氧化物（REBCO）双饼线圈的堆叠结构。在1.3G磁体中，H800是其自身SCF产生的大型误差场的主要来源。为研究场抖动技术的有效性，我们选取H800三个线圈中的两个（HCoil2与HCoil3）的NI REBCO双饼线圈各一个，将其放置于一台5T/300mm室温孔径外磁体的中心孔内。该外磁体既可用于在双饼线圈中感应SCF，也可通过场抖动过程抵消该场。每次实验中，我们在外部径向磁场Br>0的轴向位置处向双饼线圈中感应SCF，随后进行场抖动操作，移动至另一外部轴向磁场Bz远大于Br的位置。为验证其他SCF抑制技术（例如电流扫描反转法（Current-sweep-reversal, CSR））在L500与H800串联时是否仍可应用于H800，我们针对双饼线圈的其他轴向位置组合开展了类似的测试序列。本论文报道了77K下的实验结果，建立了可合理解释该实验结果的分析模型，并将该分析方法应用于1.3G磁体满功率运行时的场抖动系统设计。