engineering breakeven is the point at which a 📝fusion power plant produces more electricity than the entire facility consumes — net power measured at the plant gate rather than at the plasma boundary.
Its near-neighbor is 📝scientific breakeven, and the gap between the two is the distance between a physics milestone and a power plant. Scientific breakeven compares only fusion power against the heating power absorbed by the 📝plasma. Engineering breakeven counts everything: the wall-plug electricity behind every heating system, the magnets and cryogenics, and the roughly two-thirds of thermal energy lost converting fusion heat into electricity. Because of those overheads, a plant needs a plasma gain — 📝Q (fusion energy gain factor) — of order 10 or more before the site as a whole comes out ahead.
No facility has yet achieved engineering breakeven. The National Ignition Facility's 2022 breakeven shot produced 3.15 megajoules of fusion energy while its lasers drew roughly 300 megajoules from the grid, and no magnetic confinement device has crossed even the scientific threshold. Engineering breakeven is nonetheless the definition that matters commercially: it is the line beyond which a fusion machine stops being an experiment and starts being a power source.
Engineering breakeven is the line 📝ARC is designed to cross at commercial scale — about 400 megawatts of clean power to the grid from the first plant, sited in Chesterfield County, Virginia.