Dilithium crystal chamber

The dilithium crystal chamber (or dilithium regulation chamber or matter-antimatter chamber or dilithium chamber) was a component in a starship's warp core that contained the dilithium crystals. The chamber included dilithium regulators and antiproton injection seals. Aboard starships, this chamber was located on Deck 36. An engineer on this class of ship could monitor and control the chamber from the Engineering station on the main bridge. 

The dilithium crystal chamber for the USS Enterprise (NCC-1701-D) was designed at Outpost Seran T-1 on stardate 40052. 

On the USS Voyager, Crewman Hogan's main responsiblity was to keep the dilithium chamber filled. 

Background
There are four types of dilithium chamber that have been shown to date. One was that of the starship, though exactly which component of the reactor was the chamber itself was never disclosed.

The second was used on board the original configuration of the. It was a squat cylinder with a blunt domed top in the center of main engineering. The dilithium crystals were housed in a framework that rose out of one side of the chamber.

The next was the columnar "swirl" chamber, as shown in the Constitution-class refit and the. Backstage information, including interviews with Rick Sternbach, indicate that in this model of chamber, the entirety of the column is the reaction chamber, which is lined with a layer of dilithium to moderate the reaction.

The last type is the familiar "ball" or "hub" chamber, shown throughout Star Trek: The Next Generation and Star Trek: Deep Space Nine.