Must've missed that "high temperature" before superconductor when reading. Wendelstein 7-X uses Niob-Titanium, very much not high temperature at 10K but as I understand it's the standard for applications because metals, much unlike ceramics, aren't a bugger to deal with. If there's some suitable new materials (it's been 23 years since W-7X started getting built) I doubt they'll use it unless they know it won't be an issue, just not the right thing to bet the project on. Looking at Wikipedia things >77K are still either ceramics or need >150GPa which is insane for an industrial application. Or, wait... yep there's people who use "high temperature" to mean things other that "can be cooled with nitrogen". That might be it, 20K can be done with hydrogen.