We present a test and analysis of our method of computation of the distribution of currents in bulk superconducting samples, which is sensitive to current contribution in the deep layers of the sample. The procedure is based on measurements of the magnetic field with a Hall probe, inverted by linearization and orthogonal triangularization, known as QR decomposition, of the matrix in the resulting linear system. No assumptions on the number or geometry of domains are required. The only constraint on the method is that the critical current must be homogeneous along the c-axis. Our method is applied to real 3d samples with size in the cm range and different geometries of technological interest. The propagation of errors in the general case is analysed, and we also supply a method to estimate the error in every computation, which is applied to the computed J(Jx, Jy) in the above samples.

This paper describes the dynamics of a quantum two-level system (qubit) under the influence of an environment modeled by an ensemble of random matrices. In distinction to earlier work, we consider here separable couplings and focus on a regime where the decoherence time is of the same order of magnitude than the environmental Heisenberg time. We derive an analytical expression in the linear response approximation, and study its accuracy by comparison with numerical simulations. We discuss a series of unusual properties, such as purity oscillations, strong signatures of spectral correlations (in the environment Hamiltonian), memory effects and symmetry breaking equilibrium states.

This manuscript presents a new design for superconducting linear motor (SLM). This SLM uses stacks of second generation (2G) superconducting tapes, which are responsible for replacing YBCO bulks. The proposed SLM may operate as a synchronous motor or as a hysteresis motor, depending on the load force magnitude. A small scale linear machine prototype with 2G stacks was constructed and tested to investigate the proposed SLM topology. The stator traveling magnetic field wave was represented by several Nd-Fe-B permanent magnets. A relative movement was produced between the stator and the stack, and the force was measured along the displacement. This system was also simulated by finite element method, in order to calculate the induced currents in the stack and determine the electromagnetic force. The H-formulation was used to solve the problem and a power law relation was applied to take into account the intrinsically nonlinearity of the superconductor. The simulated and measured results were in accordance. Simulated results were extrapolated, proving to be an interesting tool to scale up the motor in future projects. The proposed motor presented an estimated force density of almost 500 N/kg, which is much higher than any linear motor.

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Artificial welding of melt-textured YBCO blocks opens the door to the fabrication of large, complex-shaped pieces required for applications. In order to evaluate the superconducting quality of the welds, we have developed a Hall probe mapping system, able to record the local magnetization at 77 K under dynamic applied fields in the range of-1 to 1 T. The system was used to characterize welded samples prepared with a new Ag induced surface melting joining technique. The magnetization maps of unwelded and welded samples of various qualities are compared and discussed. The current distributions associated to the Hall maps were calculated using the Caragol software. The magnetization and current distribution maps over the joint show that good quality welds can be reached with this joining method.

A Hall probe magnetic imaging system that works in magnetic fields in the range 1 T to 1 T has been implemented, and it has been used to characterize the superconducting behavior of single domain melt textured YBa 2 Cu 3 O 7 rings. We show that in addition to the analysis of the evolution of the local magnetic field distribution when the external magnetic field is cycled, the hysteretic behavior of the magnetic moment can also be investigated after integration of the local magnetic field. The critical current density has been determined through the critical state model and it has been compared to that calculated by inversion of the Biot-Savart law. A remarkable agreement is achieved with both methods.

One of the most widespread mathematical formulations applied to simulate the electromagnetic phenomena of coated conductor in the recent literature is the H one. However, the only validation of the model has been indirect by using measurements taken from the applications, as measurements of the energy losses in ac fields, forces developed in levitation systems or any other parameter related to a specific application. Direct validation of the calculation requires the observation of the local out of plane magnetic field over the surface of the sample and this is only accessible under magnetooptical observations and, in a larger scale and better dynamic range, by the Hall scanning microscopy. We propose here the experimental validation of the Hformulation by comparing the simulated results with measurements made by a Hall probe mapping in a second generation (2G) tape sample for several DC transported currents at 77 K. The paper presents a methodology to simulate the 2G tape by using only measured data obtained from a sample and its normalized J(B) experimental curves. Some boundary conditions that allow a faster convergence of the problem are investigated. Simulated results of the 2G tape modelled considering only the 1 µm HTS layer were compared with other that represent the most important layers of the coated conductor structure in the calculations. The simulated and measured results present a good agreement, proving that this model can calculate precisely the magnetic field and, hence, the current distribution in HTS samples.

Nondestructive testing of superconducting blocks and thin films is a worth point in their development and their industrial production. The most intrinsic characteristic to be tested is the critical current, so is the maximum current can be carried in the superconducting state. The measurement of the current flowing through the samples could be done by direct transport experiments but this means using specific samples, and only the mean current may be found. Distribution of current density in the sample is more relevant because it yields the map of inhomogeneity of the samples, and its effect in the current density distribution. Magnetic measurements have been developed by Hall scanning and magneto-optical effect, allowing the mapping of the component of the magnetic field perpendicular to a surface of the sample created by the current distribution. By solving the inverse Biot-Savart problem a map of current densities can be obtained. We will present the status of the magnetic measurements obtained by exploring superconducting bulks and tapes magnetized by an external field and the magnetic map generated by the current carried through superconducting wires.