The work performed during this project covered technical issues starting from the HTS tapes, their windings, to the HTS insert design, its coupling to an LTS magnet, to finally assess the concept of an all-SC EMFL user magnet. It also covered the essential underpinning elements to leverage our design effort ultimately as a major upgrade of the EMFL facilities as the identification of the user needs, cost estimates, possible funding schemes, scenarios for their implementation in relationship with the relevant scientific cases.
Tapes from several suppliers were characterized. The critical current Ic vs. the magnetic field and its orientation is a prominent parameter in the design and dimensioning of the HTS insert as well as the turn-to-turn resistance and the degradation of Ic by strain. Other practical properties such as the delamination strength, joint resistivity and regularity of the winding were also considered to validate a tape. The final choice was a newly developed HTS tape by THEVA with an enhancement of the critical current at low temperature and high magnetic field thanks to artificial pinning. Test coils consisting of an assembly of two double HTS pancakes (named 2 DP coil) were fabricated for testing under high magnetic field close to the foreseen operating condition.
A set of simulation tools has been specifically developed, implemented and bench-marked. Designs have been then carried out, targeting 32 and 40 T, as a set of several HTS insert showing the possibility to prioritize homogeneity, peak field or bore size according to the user requirements. 40 T can be reached with a single stack of pancakes but at the sake of a narrower central space. Only a design with nested coils enables to maximize the space for experiment and to reduce constrains. A simple version was proposed to be fabricated and tested in a large bore resistive magnet as a proof of concept.
The interaction of LTS/HTS parts during a quench and the protection scheme were investigated showing the need for a mechanical reinforcement of the LTS outsert to accommodate the potential large axial forces that may be produced by a quench of the HTS insert.
The interfacing of an HTS insert within an LTS magnet was developed, providing de facto a test bench. A series of quench-test measurements using a first 2DP coil up to 19 T, provided valuable information about the HTS/LTS coupling. Closer to ultimate limits, a second 2DP even quenched at 22.6 T and triggered a quench of the LTS system at 17 T, i.e. at an inductively stored energy of ~ 5 MJ, with no damage for either coils.
Several experiments performed to test a variable temperature insert and its sample environment in such LTS/HTS configuration and a first scientific pilot experiment finalized its assessment as a user magnet.
A user survey and a subsequent workshop showed a strong interest and support of our community with a clear idea of what can be expected and done. Further workshops with other facilities were conducted for dissemination towards other communities such as neutrons, high-power lasers, far-infrared free electron lasers, XFELs and synchrotrons.
A facilities inventory was conducted for defining the functional requirements for the implementation of all-superconducting user magnets in an EMFL facility and realistically estimating their implementation costs. CNRS has already obtained a national funding to fabricate a prototype whereas HZDR may also fund an HTS insert so that two prototypes may exist in 2027 in Europe.
