First direct evidence that filament fracture accompanies degradation of superconducting cables designed for the International Thermonuclear Experimental Reactor (ITER). The tokomak fusion reactor, now under construction in France, is an international collaboration crucial to future energy generation from nuclear fusion.
Ferro-pnictide superconductors attracted immediate attention for potential applications due to their high superconducting transition temperatures (Tc up to 56 K) and high upper critical magnetic fields (Hc2 over 100 T). Unfortunately, much as in cuprates, grain boundaries (GBs) were found to obstruct their current carrying capability. This posed a serious technological problem because wires for magnets cannot be single crystals and, thus, inevitably contain grain boundaries. This work shows that low-temperature synthesis of the compound (Ba0.6K0.4)Fe2As2 (Ba-122) in the form of polycrystalline wire achieves a current density three times that of state-of-the-art Nb3Sn wires.