Attempt to Generate Uniform Magnetic Field by Face-to-Face Magnet System Containing HTS Bulk Magnets

In order to develop small-scale nuclear magnetic resonance devices, the authors have been developing uniform magnetic fields in the space between the face-to-face settled magnetic poles which contain HTS bulk magnets. Since the NMR magnets in general require highly uniform field, it was expected to be difficult to form such homogeneous magnetic-field distribution with use of HTS bulk magnet, because the bulk magnets is characterized by its inhomogeneous magnetic field showing steep gradient. The authors modified the shape of the field distribution from convex to concave by attaching an iron plate on the pole surface. Then, the magnets were then settled face-to-face with various gaps, and the magnetic-field uniformity was estimated in the space. In order to detect the NMR signals, the field uniformity less than 1,500 ppm should be required after the former results on the hollow-type magnets. When we combined the concave and convex field distributions to compensate the uneven field distributions, the best uniformity reached 358 ppm in the 30 mm gaps, which exceeded the target value. In addition, we numerically simulated the feasible performance in this configuration, which resulted in obtaining the best uniformity of 30 ppm at 1.1 T at 7 mm distant from the pole surface in the gap of 30 mm. ... mehrThis result suggested that the concave and convex magnetic field distributions compensate the field uniformity with each other with keeping the magnetic field strength in the gap.