High temperature superconductors for storage of high magnetic fields in industrial production

This work analyses the performance of samples produced using new fabrication methods, which could be very interesting for industrial production of high temperature bulk superconductors in large quantities. The first part concentrates on melt textured high temperature superconductors produced with more than one seed crystal. This method leads to shorter crystallisation times. Measurements of trapped fields in these samples, as well as analysis of local parameters measured by the magnetoscan method, show that multiseeding leads to a considerable decrease of the performance. Between the growth sector boundaries of the seeds an aggregation of second phase inclusions is formed which represents a significant barrier for the critical current and therefore decreases the trapped field. The second part analyses Gd-123 superconductors, which can be produced under normal pressure and in normal atmosphere. Measurements show positive properties, such as higher values of Tc, Jc, Birr and therefore trapped field, of Gd-123 compared with standard Y-123 superconductors. Using a new mixture, these benefits can be transferred to conventional production methods. Furthermore it was shown that doping with Gd-2411(Bi) nano particles, which are additional pinning centers for magnetic flux lines, increases the maximum trapped field. However the particles are not distributed homogeneously in the first layer under the seed crystal. In the course of this research the magnetoscan technique was adapted for Jc measurements, giving a very viable non-destructive and fast method to characterise high temperature bulk superconductors. (author)