The fusion reactor is a generator that makes more than three times a generator's power for twice its fuel. Like any generator it takes a generator slot, and every station allows one.
Its blueprint is locked behind research. An ARCHON unlocks it with a trialled generator design of their own that has reached a set power output; heat-proof materials such as shielding raise a design's power output. It is built from field coils, superconductors, shielding and coolant.