Journal
JOURNAL OF MAGNETIC RESONANCE
Volume 200, Issue 1, Pages 6-14Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jmr.2009.05.010
Keywords
Nuclear magnetic resonance; Rotating micro-coils; Eddy currents; Lead nitrate; Chemical shift thermometry; Finite elements calculations; Magic angle coil spinning; MACS
Funding
- European Research Council [FP7/2007-2013]
- Agence Nationale de la Recherche [ANR-06-JCJ0061]
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The application of nuclear magnetic resonance (NMR) to systems of limited quantity has stimulated the use of micro-coils (diameter <1 mm). One method recently proposed for the union of micro-coils with Magic Angle sample Spinning (MAS), involves the integration of a tuned micro-coil circuit within standard MAS rotors inductively coupled to the MAS probe coil, termed magic-angle coil spinning (MACS). The spinning of conductive materials results in the creation of circulating Foucault (eddy) currents, which generate heat. We report the first data acquired with a 4 mm MACS system and spinning up to 10 kHz. The need to spin faster necessitates improved methods to control heating. We propose an approximate solution to calculate the power losses (heat) from the eddy currents for a solenoidal coil, in order to provide insight into the functional dependencies of Foucault currents. Experimental tests of the dependencies reveal conditions which result in reduced sample heating and negligible temperature distributions over the sample volume. (C) 2009 Elsevier Inc. All rights reserved.
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