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).
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