Fast-Ramped Superconducting Dipoles for NMR Studies of Awake Animals

At present, functional NMR studies of metabolic processes, which require repeated images taken over a period of time, are only performed on sedated animals. This is because the axes defined by the main NMR solenoid field and the time varying gradient magnets used for spatial encoding are fixed and cannot follow the motion of an awake animal. Construction and test results will be presented for a pair of superconducting dipole coils built to make possible NMR studies of animals that are awake by providing a dynamically variable orientation of the NMR field. Each dipole coil was wound from a single cylindrical layer of Nb-Ti cable with a cos-theta distribution. One coil was wound over the other and oriented so that the fields are perpendicular. The coil pair can then produce fields in any direction perpendicular to that of the main solenoid. When powered together, the dipole and solenoid fields would allow the NMR axis to vary with time and, thus, track the motion of an awake animal. A 1 m-long pair of coils was successfully ramped to the design field, 0.08 T, at the high rate (~25 T/s) needed to track the motion. Measurements of the field quality were made during the ramping. The ramp rate studies and the magnetic field measurements are reported.