SUPERCONDUCTOR FLUX PUMP FOR HIGH-RESOLUTION NMR MAGNETS

拟议的2年计划的具体目标是开发和操作一种高温超导（HTS）通量泵，该泵符合用于高场NMR磁体的HTS插入件的性能规格。 我们建议：1）搭建高温超导磁通泵，其主要部件均采用Bi-2223/银复合带材，2）与具有可比参数的Nb-Ti测试线圈耦合运行（自感1.43 H，中心场3.3 T;工作电流100 A），空间场均匀性除外，与典型HTS插入物的空间场均匀性相比，在强制衰减率下工作（10- 100 ppm/h）;和3）成功地证明了泵将衰减场转化为有效持久场（小于0.1 ppm/h）的能力。 该项目的关键里程碑如下：第一年1）完成HTS通量泵; 2）完成Nb-Ti测试线圈;以及3）Nb-Ti线圈单独以其自然（持续）模式和强制场衰减模式运行，其速率由插入电路的电阻器控制。第二年1）组装流量泵操作实验; 2）成功操作流量泵并测量其性能。关键实验变量包括：1）通量泵的操作温度（背景场将基本上为零）; 2）Nb-Ti测试线圈场衰减速率;以及3）脉冲速率。 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）操作温度上限;以及3）通量泵对液氦的总热负荷。该项目的意义在于证明了高温超导通量泵能够实现低于0.1 ppm/h的场衰减率，高温超导插入线圈具有10 ppm/h或更高的固有衰减率-对于高分辨率NMR光谱法来说太高了。该项目的成功将使HTS插入下一代高场NMR超导磁体的重要组件。

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.