High-Temperature Superconductors (HTS)
HTS has zero resistance when substantially cooled, allowing carrying high current and can be used to create magnets to produce ultra-high magnetic fields. Benefits of HTS is that it reduces heat loss when compared to copper and that it can enable compact high-field applications. This project focuses on REBCO HTS which is often referred to as coated conductor coming in a ribbon-like material stack. A compact high-field magnet typically requires kilometers of REBCO coated conductors. HTS tapes often exhibit critical current (Ic) fluctuations along the tape length. Defects in the HTS tapes introduced during manufacturing can go unnoticed and contribute as weak points prone to quench initiation. An Ic examination technique for HTS tapes is necessary for manufacturers’ quality control and users’ utilization safety.
Reel-to-Reel Inspection System for HTS
As shown in Figure 1, the inspection starts with the HTS tape unwound from the left spool, then submerged into a cryogenic bath (liquid nitrogen) to enter a superconducting state. Passing through the exciting magnetic circuit (EMC), where a magnetic field is applied to induce a persisting screening current in the HTS tape; and then the detecting magnetic circuit (DMC) which has a Hall sensor, detects the integrated magnitude of the trapped magnetic field, i.e. magnetic moment, in the tape. The magnetic field readings can be converted into local critical current on the HTS tape, identifying the weak spots and obtaining the Ic profile along tape length.
Figure 1
It is worth mentioning that identifying these weak spots is necessary to prevent the HTS conductor from quitting superconducting state due to localized overheating. Such phenomenon is well-known as ‘quench,’ often disastrous for an HTS magnet system.
HTS Coil Winding Machine
To create HTS magnets from HTS tape, a winding table will be used. During the winding process, the motors will maintain a precisely controlled tension monitored by tension sensors. The table will be made of t-slotted aluminum extrusion which allows it to be modular. This modularity allows magnets to be wound either using a single conductor, or co-wound by multiple tapes to allow current sharing or mechanical reinforcement.