DEMO is the class of demonstration 📝fusion power plants planned as the step between 📝ITER and 📝commercial fusion in public roadmaps — the first machines intended to put net electricity on the grid.
DEMO names a role, not a machine. Each major fusion program carries its own version: the European Union's EU DEMO, targeted at 300 to 500 megawatts of net electricity; Japan's JA DEMO; Korea's K-DEMO; and China's CFETR, which fills the equivalent slot. The near-neighbor distinction is with ITER itself. ITER is an experiment — its 500 megawatts of fusion power will be dispersed as heat, never converted, and its site will consume more electricity than its 📝plasma produces. A DEMO must do everything ITER deliberately defers: convert fusion heat to electricity, breed its own 📝tritium at a ratio above one, and run with the availability of a power station rather than the duty cycle of an experiment.
In the public roadmaps, DEMO designs are largely paper machines awaiting ITER's burning-plasma results, with operation generally envisioned for mid-century. That sequencing is the industry's live argument: privately financed fusion companies are building pilot plants intended to compress the ITER-to-DEMO ladder into a single generation of smaller machines, betting that stronger magnetic fields can substitute for size and decades. Whether the path to fusion electricity runs through a state DEMO program, a private pilot plant, or both is among the defining open questions of the field's next two decades.