Dilithium crystal converter assembly

From Memory Alpha, the free Star Trek reference

A dilithium crystal converter assembly (also known as the dilithium circuit or simply converter assembly) was an engineering component aboard Constitution-class starships, in use from the mid-2260s.

Dilithium (or lithium) crystals installed in the converter assembly served as a critical component of the warp drive and as a power source. A damaged converter assembly, or drained crystals, could prevent a starship from something as small as being unable to create a by-pass circuit, to something as complicated as maintaining orbit or engaging the warp drive. Dilithium in-use, and the assembly itself, could be damaged from a sustained exertion of the ship's power. (TOS: "Mudd's Women", "The Alternative Factor", "The Paradise Syndrome", "Elaan of Troyius")

The Dilithium crystal chamber and articulation frame of Galaxy-class starships appear to be a 24th century equivalent to this component.