> Their problem is all the rare earths The fraction of mass in a HTS magnet that is rare earth is surprisingly small. Most of the mass is mechanical support,

> Their problem is all the rare earths The fraction of mass in a HTS magnet that is rare earth is surprisingly small. Most of the mass is mechanical support, or substrate on which the thin HTS film is deposited. The entire ARC reactor might contain 10 kilograms of REBCO (2015 paper), out of a reactor mass of over 7 gigagrams. https://arxiv.org/pdf/1409.3540 https://arxiv.org/pdf/1409.3540