The most promising high-temperature superconductors for applications are coated conductors. These superconductors are very thin, which influences strongly their magnetic properties. Due to high AC losses, striation is required, so when reducing the surface of superconducting strips, for example, from 1 single string to 4, the magnetic moment also decreases, reducing the hysteresis losses of the tape. Due to the fabrication process to divide the tape into several strings, normally laser ablation, residual material rests between the superconducting filaments, acting as a normal conductor. The laser gap is normally around 20 μm width. This configuration permits the big currents flow across the tape in the case that a superconducting string breaks, avoiding a hot point that would burn the tape with the consequent substitution of the tape which is not always an easy task depending on the application or where the SC tape is located.
Another main reason because of the presence of the normal conductor connection string is that it actually has benefits because it gives a higher thermal stability in front of fluctuations and stabilizes the critical current. However, when there is a higher resistivity, the coupling effect decreases. Connecting superconductor filaments with normal conductor creates energy losses (coupling loss).
This diploma work is intended to develop from the beginning a computer program to calculate the magnetic properties of thin superconductors under low applied magnetic fields. The main steps of the work will be the following:
1. Computer program that calculates the magnetic field and vector potential generated by a single rectangular tape with a given current density. The main task is to settle up the tape discretization.
2. Calculate the current density in the aforementioned rectangular tape under the effect of a uniform sinusoidal applied magnetic field in the steady state situation. The superconductor is approximated as a material with zero resistivity.
3. Study the effect of joining several superconducting strips side-by-side by a material with higher resistivity, for instance that of copper. In particular, the program calculates at least the current density, the dissipated energy (called coupling loss) and the magnetic field at particular points.
4. Discuss the influence of the coupling loss at several frequencies typical for different applications, of a tape divided into 4 superconducting strips and 20 μm of copper in between.
