I found it odd that they call it high-temperature, but then perform all their experiments at 4.2 K. Also, at 4.2 K, the magnet performs worse than established Nb-Ti technology, so it doesn't seem to be a significant advancement.
High-temperature superconductor refers to the critical temperature at zero field. But the crucial field decreases sharply with temperature, so the superconducting phase appears concave on a T–B phase diagram. Therefore, in order to operate superconducting magnets at high field, liquid helium is necessary irrespective of the superconducting transition temperature (critical temperature).
Liquid hydrogen cooled superconductors (20K) would be good especially if we manage to use some materials that don't suffer hydrogen embrittlement processed/machined economically enough to really play out the cost benefits of not relying on the rare noble gas.
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