Since the discovery and development of adequate superconducting materials, the development of motors has been a challenge for applications. The basis of design, however, has been the substitution of copper wires by superconducting tapes in coils in order to obtain a higher working field, thus improving power density and efficiency.In the case of high-power motors, the benefit is clear. The cost of the materials, cryogenics and building procedures could be assumed by the clear benefit in size, weight, efficiency, and, in some cases, reliability. Otherwise, low-power motors require a different treatment. Superconducting wires are insufficiently developed to produce small coils for a high field with the adequate shape. Air gaps are more critical than in large motors and cost has a major impact. Only very specific applications, in which standard technology cannot give a reliable and satisfactory solution, could benefit from superconductivity. This paper summarizes our work realized by applying superconducting pellets in low-power motors, thus improving their power density, reliability, dynamics and regularity. Applications to cryogenics, control and high speed have been our focus.

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High-temperature superconducting artificially structured bulk samples, such as bulks with slanted drills or welds of different pieces along the c-axis with holes drilled in different asymmetric positions, pose a challenge for the computation of critical current maps able to spot the position of inhomogeneities, as they combine a current map in every ab-plane adapted to the drill/welding structure with the dependence of this structure on the position along the caxis. We improve and adapt our technique of Hall probe field measurement, discretization and QR inversion to this problem by measuring the magnetic field on top and bottom of the bulk sample to obtain some spatial resolution of the current. To test our technique we apply it to both simulations with asymmetrical geometry and a real artificially structured bulk samples.

A two-sided inverse Biot-Savart algorithm for the computation of critical current distributions in High Temperature Superconductor (HTS) pellets is introduced. It is based on simultaneous measurement of the magnetic field on top and bottom of the bulk sample with a double Hall probe, and the authors' discretization and QR inversion scheme. It yields current maps which are detailed in the ab-plane for each half of the bulk sample along the c-axis. The computed current is a O(1/z)-weighted average of the real current along the c-axis over each slice. This is the best possible resolution for current maps along the c-axis, regardless of inversion scheme.We demonstrate the new procedure by analyzing a non-c-homogeneous simulation and a real HTS pellet of cylindrical geometry with asymmetrically drilled holes on both faces.Index Terms-Critical current maps, hall magnetometry, HTS bulk samples, inverse Biot-Savart problem.

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