target gain

Fusion results are usually reported as a ratio, and everything depends on which two numbers are being divided. The measure normally quoted is what Lawrence Livermore National Laboratory calls target gain: the fusion energy released divided by the laser energy delivered to the target. The laboratory defines achieving ignition as producing more fusion energy than the amount of laser energy delivered to the NIF target, and its December 2022 shot produced 3.15 megajoules of fusion energy from 2.05 megajoules of laser energy on target, a gain of about 1.5.

That is a real physics milestone and it is also a narrow accounting. It counts only the energy that reached the fuel, not the energy needed to produce it. The lasers themselves are extremely inefficient, and the facility drew roughly 300 to 400 megajoules out of the electrical grid to deliver those 2.05. Measured from the wall socket rather than the target, the experiment consumed vastly more than it released and remains far from breaking even.

Both figures are honest as long as they are labelled, and the laboratory is explicit that the facility was not designed to be energy efficient, it was designed to demonstrate scientific break-even. The confusion arises when a target gain above 1 is reported as fusion producing more energy than it consumes. It does not yet. You may also see this ratio called scientific gain, which is common shorthand rather than the laboratory's own term.