フラックスポンプによる600 MHz NMRマグネットのドリフト補償

抄録

Although high-T_c superconductors (HTS) are very promising for high-field generation over 25 T, it is difficult to apply them to NMR magnets because of their low index values and the difficulty caused by superconducting joints. It appears that the present properties of HTS cause poor magnetic-field stability in persistent-mode operation. We applied drift compensation based on flux-pump technology to a 600 MHz NMR magnet that had a poor magnetic-field stability of about -0.7 ppm/h. The drift compensation unit consisted of nested inner (secondary) and outer (primary) coils. The inner coil was connected in series to the main coil circuits, and the outer coil was connected to the auxiliary power supply to sweep the output current very slowly. While the current of the outer coil was changed at an adequate sweep rate by the power supply, a current was induced in the inner coil by inductive coupling. The induced current canceled out the decay of the main coil current that caused by the poor drift of the magnet.