title: Experimental and numerical examination of eddy (Foucault) currents in rotating micro-coils: Generation of heat and its impact on sample temperature.
abstract: The application of nuclear magnetic resonance (NMR) to systems of limited quantity has stimulated the use of micro-coils (diameter <1mm). 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 4mm MACS system and spinning up to 10kHz. 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.
authors.affiliation: Commissariat à l'Energie Atomique, IRAMIS, Service Interdisciplinaire sur les Systèmes Moléculaires et les Matériaux, F-91191 Gif-sur-Yvette, France.
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Aguiar
authors.forename: Jacques-François
authors.initials: JF
authors.lastname: Jacquinot
authors.forename: Dimitris
authors.initials: D
authors.lastname: Sakellariou
mesh_terms: D000465:Algorithms; D004574:Electromagnetic Fields; D004735:Energy Transfer; D006358:Hot Temperature; D007856:Lead Radioisotopes; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation*; D008962:Models, Theoretical; D013696:Temperature; D013821:Thermometers
chemical_list: D007856:Lead Radioisotopes