Engineering gain (Q_E).

Fusion has two 'gains'. Scientific gain (Q) compares fusion power to heating power. Engineering gain (Q_E) compares net electricity out to electricity in — and it is the one a grid cares about.

Scientific gain Q

Fusion power ÷ heating power

Engineering gain Q_E

Net electricity out ÷ electricity in

Breeder

Q 3.424 (scientific gain)

Burner

Q_E 1.31 at the frozen Mode M point

A plasma can have a high scientific gain and still not power a plant, because turning fusion power into electricity and running the machine both take energy. Engineering gain accounts for all of it: it is the net electricity delivered divided by the electricity consumed. Q_E > 1 is the threshold for a real generator.

The Kronos machines report both honestly. The breeder is quoted at its scientific gain (Q 3.424) because its job is gain and breeding. The burner is quoted at its engineering gain — Q_E 1.31 at the Mode M closing point — because as a power plant that is the number that counts. Direct energy conversion is what lifts the burner's Q_E above 1.