Eddy Currents in Pulsed Field Measurements

R. Grössinger, M. Küpferling, P. Kasperkovitz, A. Wimmer, M.Taraba, W.Scholz, J.Dudding, P. Lethuillier, J.C.Toussaint, B. Enzberg-Mahlke, W.Fernengel, G. Reyne

J.M.M.M. (2001) submitted to JEMS'01 Conf. Grenoble Aug. 2001, paper E116.

In pulsed field magnetometry the error due to the magnetization of eddy currents is a serious problem. Therefore systematic experimental and theoretical studies of the magnetization due to eddy currents in metallic samples were performed. Eddy current measurements were performed in cylindrical and spherical samples of Cu and Al. The eddy currents were determined by magnetization measurements using two different pulse durations (9.1 ms and 15.7ms) and applying a bipolar field with an amplitude of 5.2 T. The samples were measured in the as cast state (after machining) as well as after a heat treatment (400t = 2h). The eddy currents were analyzed in three different ways:
i) Analytical calculation of the eddy currents in metallic spherical samples agrees with the experiment within 10%.
ii) The "eddy current" magnetization as a function of dH/dt exhibits a linear dependence. Analytic calculations proofs that the slope is proportional to the specific resistivity of the material.
iii) The eddy currents were also analyzed using a 2D-software package called FEMM. The shape of the magnetization due to the eddy currents showed theoretically and experimentally the same shape.

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Oct. 5, 2001