AC Magnetic Measurements on Superconductors: Design of a Device for Magneto-Thermal Measurements

AC Magnetic Measurements on Superconductors: Design of a Device for Magneto-Thermal Measurements

Philippe Laurent (University of Liège, Belgium), Jean-François Fagnard (University of Liège, Belgium) and Philippe Vanderbemden (University of Liège, Belgium)
DOI: 10.4018/ijmtie.2011070105
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This work describes the design and realisation of an apparatus to measure simultaneously the AC magnetic properties and the temperature distribution on the top surface of bulk superconducting samples (up to 32 mm in diameter) in cryogenic conditions (temperature range 78-120 K). First the authors describe the experimental set-up used for simultaneous thermal and magnetic characterization of the sample. Next, the authors describe the practical considerations required for generating the large AC magnetic fields, possibly in the presence of DC fields. Then the authors present the data acquisition system allowing both temperature and magnetic data to be recorded at high a sampling rate." The performances and limitations of the system are discussed.
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2. Instrumentation Of The Superconducting Sample

Basically, a susceptometer consists of a magnetizing (primary) coil and two pick-up (secondary) coils wound electrically in series opposition (Nikolo, 1995). The electro-motive force (emf) induced across ideal pick-up coils (i.e., wound with the same number of turns and in identical geometries) is zero in the absence of a sample. Inserting a magnetic sample centred in one of the secondary coils results in the generation of a non-zero signal that is directly proportional to the AC magnetic susceptibility.

In the experiment described here, the classical set-up is extended to measure simultaneously (i) the temperature against the top surface of the superconducting sample and (ii) the magnetic flux density against the bottom surface of the sample, as shown in Figure 1. In the following we describe the temperature sensors and the magnetic sensors.

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