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Highest magnetic field insert coil made from high temperature superconductors for a 25 Tesla break-through (HIGINS)

Final Report Summary - HIGINS (Highest Magnetic field insert coil made from high temperature superconductors for a 25 Tesla break-through)

Europe leads the world in the supply of Superconducting Magnets with several successful manufacturers based with the EU. The HIGGINS project has successfully developed a new technology and allowed the production of a magnet using novel material to achieve a highly advantageous performance. This development would help to keep European companies at the forefront of superconducting magnet technology.

The project was to develop high performance BISCO conductors and use them to build a breakthrough 25 Tesla magnet.

There were two distinct parts to the project. First to produce conductors at Trithor and test them at IFW. The second part being to build the magnet consisting of an LTS background coil and the HTS (BISCO) insert coils to be installed and tested at Cambridge.

The insert coils were to be a 1st trial and 2nd improved set and this was what happened. The first coils were built using conductor from Trithor and these were used to trial production methods. A second set of coils was then made which have been installed in the LTS outer coil and delivered to Cambridge.

The initial concept was a very large LTS but this would have had a very large stray field and would not be suitable for installation within the existing building at the Department of Engineering at Cambridge. The coil chosen provides 14 Tesla in a 140mm bore.

The main issues in producing high field coils were the current density, the stress / strain level and protection issues when the coil transitions to the normal state.

Test of the coil transition to the normal state demonstrated a slow transition which implied that coil is self-protecting during transition. This left the issue of mechanical strength. As produced the conductor was supported by a stainless steel strength element producing a material of considerable strength however, the forces in ultrahigh field magnet were extreme and was necessary to provide additional support. This was provided by external coil supports machined from solid stainless steel.

Exploitation of the research and development work would be carried out by the three commercial participants: Trithor 2 would continue to develop high performance tape conductors and their applications. Techtra would continue development and sale of silver alloys and tubes. Cryogenic Ltd would build and sell further ultra high field magnets using the know-how gained during the project.

The magnet built during the project would be made available free to members of the consortium and on a modest chargeable basis to researchers from Europe and around the world. With a magnetic field of 18 to 19 Tesla at 4.2 K, the magnet represented one of the highest steady fields available. Research in several other fields was also being planned to take advantage of the high magnetic field facility.

The market for very high field magnets is significant. It is driven by the needs of research at fields of 20 Tesla and above. It is constrained by the high costs and technical difficulties of working at these fields. Cryogenic would exploit the success of the Higgins magnet to address this research market with the intention of extending the market into new applications involving NMR at very high frequencies of 1 gigaHz and above as well as MRI in lower fields.

While the field achieved by this magnet was not higher than the field that could be achieved with LTS conductors at 4.2 K it demonstrated the practicality of the approach. Furthermore new 2nd generation YBCO conductors with up to four times the current density started to become available and with these conductors a field of 25 Tesla appeared practical for this magnet provided the windings could be designed in such a way as to support the forces involved.

A magnet of 25 Tesla which is all superconducting would have unique advantages compared to the hybrid alternative. Firstly, both capital and running costs are very much lower. Secondly, the field is more stable and quieter. It would also be possible to make the magnet of high homogeneity more easily. Ideally, a true persistant coil would be made however this could be difficult due to flux creep in the HTS material as well as the difficulty of making superconducting joints to HTS materials.