Selective Magnetic Field Invasion into HTS Bulk Magnets in Pulse Field Magnetizing Processes

The magnetic flux invasion into the Dy123-based HTS bulk magnets were experimentally evaluated during the pulsed field magnetization processes. Since the invasion of the magnetic flux into the sample would be expected to be affected by the $J-{c}$ distribution, we estimated the differences of the magnetic flux motions between the growth sector boundary (GSB) and the growth sector region (GSR) by measuring the changes of magnetic flux density and temperature during the pulsed field application of 5 T at 30 K. The experimental results on the temperature measurement showed that the magnetic flux invades into the sample through the path in the GSR prior to that in the GRB region. Furthermore, the changing rate of magnetic flux gradually changed with the position on the GSR, while they irregularly changed and did not exhibited any tendency on the GSB. This means that the magnetic flux straightly invades the sample from GSR heading for the center portion, while it does not uniformly flow on the GRB. As a result, the heat generation occurs in the GSR area prior to the GSB region. The magnetic flux invasion behavior exhibits selective and nonuniform motion, reflecting the difference of the macrostructure on the GSR and the GSB.