Field performance of a prototype compact YBCO "annulus" magnet for micro-NMR spectroscopy

Area of Science:

• Superconducting Magnet Technology
• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science

Background:

• Development of compact superconducting magnets is crucial for advancing NMR spectroscopy.
• Yttrium Barium Copper Oxide (YBCO) offers high-temperature superconductivity, enabling operation at less extreme cryogenic conditions.
• Previous research has explored YBCO magnets, but direct comparisons of performance at 77 K and 4.2 K are limited.

Purpose of the Study:

• To construct and test a prototype compact annulus YBCO magnet (YP1070) for micro-NMR spectroscopy.
• To compare the performance of the YP1070 magnet at liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures.
• To evaluate key NMR magnet parameters: trapped field strength, spatial field homogeneity, and temporal stability.

Main Methods:

• Fabrication of the YP1070 magnet using a stack of 1070 thin YBCO plates.
• Field-cooling the magnet at 77 K (liquid nitrogen) with background fields of 0.3 T and 1 T.
• Field-cooling the magnet at 4.2 K (liquid helium) with background fields of 2.8 T and 5 T.
• Measurement of trapped field strength, spatial field homogeneity, and temporal stability at both temperatures.

Main Results:

• At 4.2 K, a maximum peak trapped field of 4.0 T (170 MHz 1H NMR) was achieved with ~3000 ppm homogeneity.
• The magnet achieved its best homogeneity of 182 ppm at 2.75 T (117 MHz).
• Peak trapped fields at 4.2 K were approximately 10 times higher than at 77 K, correlating with YBCO's enhanced current-carrying capacity.
• Temporal stability at 77 K degraded with increasing trapped field strength (110 ppm/h at 0.3 T vs. 17,500 ppm/h at 1 T).
• Temporal enhancement of trapped fields at 4.2 K was observed for the first time.

Conclusions:

• The YP1070 YBCO magnet demonstrates significantly improved performance at 4.2 K compared to 77 K, particularly in trapped field strength.
• The results highlight the potential of YBCO magnets for high-field NMR spectroscopy, with 4.2 K operation offering superior field generation.
• Further research into optimizing YBCO magnet design and operating conditions is warranted to enhance both field strength and homogeneity for practical NMR applications.