SUPERCONDUCTOR FLUX PUMP FOR HIGH-RESOLUTION NMR MAGNETS

拟议的两年计划的具体目标是开发和运行一种高温超导(HTS)磁通泵，该泵满足用于高场核磁共振磁体的高温超导插件的性能规格。我们建议：1)建造一个高温超导磁通泵，其主要部件都将由Bi2223/银复合带材制成；2)将其与Nb-Ti测试线圈耦合运行，其参数(自感1.43H；中心磁场3.3T；工作电流100A)与典型高温超导插件的磁场均匀性(空间场均匀性除外)，工作在强制衰减率(10-100ppm/h)下；以及3)成功地展示了泵将衰减场转变为有效持久的能力(小于0.1ppm/h)。该项目的主要里程碑如下：第一年1)完成高温超导磁通泵；2)完成Nb-Ti测试线圈；3)Nb-Ti线圈单独在其自然(持久)模式和强制场衰减模式下运行，速度由插入电路的电阻控制。第2年1)流量泵运行实验组装；2)流量泵成功运行并进行性能测试。主要实验变量包括：1)流量泵的工作温度(背景场将基本为零)；2)Nb-Ti试验线圈场衰减率；3)脉冲速率。泵的性能评估将基于：1)在给定的强迫场衰减下测量的有效场衰减率；2)运行温度上限；以及3)通量泵对液氦的总热负荷。该项目的重要意义在于展示了高温超导磁通泵的现场衰减率低于0.1ppm/h的能力，而高温超导插入线圈的固有衰减率为10ppm/h或更高-对于高分辨率核磁共振光谱分析来说太高了。该项目的成功应该会使HTS为下一代高场核磁共振超导磁体插入至关重要的部件。

The specific aim of the proposed 2-year program is to develop and operate a high-temperature superconductor (HTS) flux pump that meets performance specifications for use in an HTS insert for high-field NMR magnets. We propose to: 1) build an HTS flux pump, chief components of which will all be built with Bi-2223/silver composite tape; 2) operate it coupled with a Nb-Ti test coil, of comparable parameters (self inductance 1.43 H; central field 3.3 T; operating current 100 A), except spatial field homogeneity, with those of a typical HTS insert, operating at forced decay rates (10--100 ppm/h); and 3) successfully demonstrate the pump's ability to transform the decaying field to effectively persistent (less than 0.1 ppm/h). The project's key milestones are as follows: 1st Year 1) Completion of the HTS flux pump; 2) completion of the Nb-Ti test coil; and 3) operation of the Nb-Ti coil alone in its natural (persistent) mode and in forced field-decaying mode with the rate controlled by a resistor inserted into the circuit. 2nd Year 1) Assembly of the experiment for flux pump operation; 2) successful operation of the flux pump and measurement of its performance. Key experimental variables include: 1) flux pump's operating temperature (background field will be essentially zero); 2) Nb-Ti test coil field decay rate; and 3) pulsing rate. The pump's performance evaluation will be based on: 1) measured effective field decay rate for a given forced field decay; 2) upper operating temperature limit; and 3) flux pump's total thermal load on liquid helium. The project's significance is the demonstration of an HTS flux pump's ability to achieve field decay rates of less than 0.1 ppm/h with an HTS insert coil having an inherent decay rate of 10 ppm/h and higher---too high for high-resolution NMR spectrometry. The success of the project should make HTS inserts vital components for the next generation of high-field NMR superconducting magnets.