Research data supporting "Thickness Dependence of Trapped Magnetic Fields in Machined Bulk MgB₂ Superconductors"

A summary of the research data supporting "Thickness Dependence of Trapped Magnetic Fields in Machined Bulk MgB2 Superconductors" (https://doi.org/10.1109/TASC.2022.3147140). The dataset related to this publication ("MgB2 bulk thickness data_MA_26-1-2022.xlsx") can be opened in Microsoft Excel and is available at https://doi.org/10.17863/CAM.74840 Sheet 1: Jc(B) @ 20 K The assumed Jc(B, 20 K) characteristics for the numerical models, shown in Fig. 2 of the manuscript, based on experimental data for small specimens taken from one of the unmachined bulks (‘pre-machining Jc’ = Jc,pre) and from the final machined bulk (‘post-machining Jc’ = Jc,post). Jc of the small specimens – cut from the centre of the bulks with typical dimensions of 1 × 1 × 0.5 mm^3 – was calculated from the width of the magnetization hysteresis loops measured using a SQUID magnetometer (Quantum Design: MPMS-XL5s). This calculation is based on the extended Bean model (see main manuscript). The data is input into the model using a direct interpolation. Sheet 2: Trapped Field Data The trapped field data presented in Figs. 3 and 5 of the manuscript for T = 20 K. Also included are the trapped field data for T = 5, 10 and 15 K (not presented in the manuscript). The experimental data were measured using transversal cryogenic Hall sensors (HGCT-3020, Lake Shore) at the centre of both surfaces (machined and unmachined). The modelling data were obtained from COMSOL Multiphysics (see manuscript for details) and given for t = 0 and t = +10 min (to allow for flux creep, as presented in Figs. 3 and 5) for the three Jc assumptions: Jc,post, Jc,pre and Jc,mod (see equation (3) in the manuscript). Sheet 3: Analytical Results These data were derived from the analytical equation, given by equation (2) in the manuscript, based on Bean's critical state model and application of the Biot-Savart law. The equation calculates the magnetic flux density at any height, z, above a superconducting disc of radius, a, carrying an induced, persistent supercurrent of constant critical current density, Jc, taking into account the finite thickness of the bulk, t. The data are calculated from the trapped field for the unprocessed / unmachined bulk of thickness 20.243 mm at T = 20 K, for z = 0 (the centre of the top surface of the bulk) and z = +0.5 mm (slightly above the top surface, taking into account the active region of the Hall sensor; presented in Fig. 3).