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.
