Colloquia

Samenvatting

The rising demand for electricity is driving research into alternative energy sources. Fusion energy is a promising candidate for providing unlimited and clean power. Tokamak-type fusion devices require high magnetic fields, which need High-Temperature Superconductors (HTS). These superconductors must withstand significant electromagnetic and thermal loads, requiring careful analysis and design to ensure stable operation.

In order to investigate the electromechanical properties of HTS-tapes, a measurement setup called TARSIS (Test ARrangement for Strain Influence on Strands) has been constructed at EMS at the University of Twente.

This thesis looks into some issues with the TARSIS and either fixes them or suggests measures that could be taken to resolve them. To solve an error in the measured stress and strain, some parts were replaced and the instrumentation was recalibrated.

A second issue was the sudden quenching of tape samples with copper layers thinner than 10 μm. Based on recommendations from previous work a COMSOL 3D multi-physics simulation of the measurement was developed to investigate the thermal, mechanical and electrical effects in the set-up that might cause a quench. The model proves that in the conditions of a typical measurement, the peak temperature and axial strain in the tape are both at the edges of the clamps, the area where quenches occur during real experiments. Since both of high temperature and strain can negatively affect the critical current, this aligns with what is seen during experiments. The high temperature in this location is a result of the ohmic heating due to the contact resistance between the clamp and the tape. The strain peak is partly due to bending of the tape due to clamp pressure, but increases drastically when applying displacement. To decrease the chance of quenches, there are multiple next steps that can be taken, such as improving contact resistance, implementing local cooling elements and altering the clamp design.

The TARSIS set-up has been improved to ensure correct stress and strain measurement data. With the insight given by the model and experimental results, the TARSIS can be improved to be able to measure even thin tape samples.