A real-world high-value breakthrough in physics would be to find some substantially cheaper (than the giant tokamak approach) arrangement of matter that can cre

A real-world high-value breakthrough in physics would be to find some substantially cheaper (than the giant tokamak approach) arrangement of matter that can create sustained nuclear fusion with energy out to energy in factors over 10, which can also feasibly be built within a decade or two. Advances in astrophysics or fundamental models are all very cool but won't be of much real-world applicability, at least in the short or medium term.