Modelling thermodynamics in a high-temperature superconducting dipole magnet: An inverse problem based approach

The use of practical high temperature superconductors (HTS), REBCO tapes especially, in magnet applications has become possible thanks to the increasing interest of manufacturers. One difficulty has been the nonlinear material properties that are challenging to measure and model. To advance in such, demo systems are needed and they must be thoroughly analyzed. Recently, one of the first HTS dipole magnets was built to study the usability of REBCO Roebel cables in particle accelerator magnets. The prototype magnet Feather-M2 was designed, constructed and tested within EUCARD2 collaboration project at CERN in 2017. In the measurements, the magnet behaved in an unexpected way: the magnet was able to be operated at operation currents above the maximum current that was predicted based on short-sample measurements. Additionally, unexpectedly gradual dependency between magnet's resistive voltage and operation current was observed. In this work, a thermodynamical model is formulated in order to study the behavior of Feather-M2. The model was parametrized and the parameters were solved via inverse problem by finding the best match to experimental results. Thereby insight was gained on the prospects of the utilized thermodynamical model and also on the behavior and operation conditions of the magnet via the inverse problem solutions. To summarize, this paper presents a new methodology for analyzing magnets in operation and applies it to a state-of-the-art magnet.