Despite the fact that nuclear fusion has been pursued as a power source since the 1950s, fusion reactors have yet to be effectively turned into a regular power source. Tokamaks, the first kind of fusion reactor attempted, generated power by using magnets to squeeze and heat plasma in a giant ring. To make it work, you need a massive donut-shaped vacuum chamber, and it can take years to go from construction to power generation. There has been something of a modern revival of fusion reactor attempts, but most designs still are tremendous undertakings, requiring the kinds of resources and infrastructure that usually only governments can provide. And such coordination efforts are difficult in the best of times and can be an impossible sell during severe financial constraints.