Journal
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS
Volume 469, Issue 13, Pages 694-701Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.physc.2009.02.014
Keywords
Superconducting magnet; NMR; Bi-2223; Beyond 1 GHz NMR; Field stability; Screening current-induced magnetic; Hysteresis; Relaxation; Remanent magnetic field
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The screening current-induced magnetic field in the (Bi,Pb)(2)Sr2Ca2Cu3Ox (Bi-2223) insert coil proposed for a beyond 1 GHz nuclear magnetic resonance (NMR) spectrometer may generate a long-term field drift, resulting in a loss of field-frequency lock operation and an inability to make high resolution NMR measurements. The measured screening current-induced magnetic field of a Bi-2223 double-pancake coil exhibits a hysteresis effect at 4.2 K that is reproduced by a numerical simulation based on a finite thickness rectangular superconductor bar model. The screening current-induced field at the coil center is of opposite polarity to that generated by the coil current, and thus the apparent field intensity shows a positive drift with time. On the contrary, the field at a coil end is of the same polarity as the coil field, and the apparent field intensity decreases with time. If we wait for similar to 1000 h after coil excitation. the field drift rate approaches the field decay rate of the persistent current of 10(-8) h(-1), suitable for a long-term NMR measurement in a beyond 1 GHz NMR spectrometer. (c) 2009 Elsevier B.V. All rights reserved.
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