Fusion pre-burners were a part of the matter/antimatter injector assembly on Galaxy-class starships.

When the USS Enterprise-D suffered a problem with the fuel injectors, Geordi La Forge tried to perform a magnetic quench on the pre-burners to reset the injectors' magnetic fields. During a later brainstorming session in engineering with the senior engineering staff in an attempt to solve the problem, Duffy suggested the same thing, however La Forge replied that had already tried the procedure, and it had failed. (TNG: "Hollow Pursuits")