SUPERCONDUCTOR FLUX PUMP FOR HIGH-RESOLUTION NMR MAGNETS

这项为期2年的计划的具体目标是开发和运行一种高温超导体（HTS）磁通泵，该泵符合用于高场核磁共振磁体的高温超导体插入件的性能规范。我们建议：1)构建一个高温超导磁通泵，其主要部件全部采用Bi-2223/银复合胶带；2)与Nb-Ti测试线圈一起工作，其参数（自感1.43 H，中心磁场3.3 T，工作电流100 a）可与典型的高温超导插入线圈相比较，除了空间场均匀性外，工作在强制衰减率（10- 100 ppm/ H）下；3)成功演示了泵将衰变场转化为有效持久（小于0.1 ppm/h）的能力。该项目的主要里程碑如下：第一年1)完成HTS通量泵；2)完成Nb-Ti测试线圈；3) Nb-Ti线圈单独在自然（持久）模式和强制场衰减模式下工作，其速率由插入电路的电阻控制。1)通量泵运行实验的组装；2)流量泵的成功运行及其性能的测量。关键实验变量包括：1)流量泵工作温度（本底场基本为零）；2) Nb-Ti测试线圈场衰减率；3)脉搏率。泵的性能评估将基于：1)给定强制场衰减的测量有效场衰减率；2)工作温度上限；(3)通量泵对液氦的总热负荷。该项目的重要意义在于证明了HTS通量泵能够实现小于0.1 ppm/h的场衰减率，而HTS插入线圈的固有衰减率为10 ppm/h甚至更高，这对于高分辨率核磁共振光谱来说太高了。该项目的成功将使高温超导磁体成为下一代高场核磁共振超导磁体的重要组成部分。

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.