Operation of a 130-MHz/9-mm Compact HTS Annulus Magnet With a Micro-NMR Probe

In this paper, we report final operation results of our compact annulus NMR magnet, named YP2800, with a homemade micro-NMR probe in a bath of liquid helium at 4.2 K. YP2800 comprises of a stack of 2800 YBCO "plate annuli," 0.08 mm thick, either 46 mm or 40 mm square, each having a 26-mm hole machined at the center. By the field-cooling technique, YP2800 was energized at 130 MHz (3.05 T); an overall peak-to-peak homogeneity of 487 ppm within |z| < 5 mm was measured at a moment when a field drift of 11 ppm/h was reached in three days after field cooling. Due to a small (9.2 mm) bore size, no commercial probes could fit into the bore; an 8.5-mm micro-NMR probe was designed and constructed. Following a general description of YP2800 and design construction details of the micro probe, this paper presents NMR signals captured by the probe for a dimethyl sulfoxide sample of ϕ 4.4 and 5 mm long at a base frequency of 130 MHz with a half-peak width of 60 kHz; the corresponding frequency impurity of 461 ppm is chiefly due to a spatial field error, i.e., 487 ppm in the target space.