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

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