MAIS display

The system displayed on a monitor of the Enterprise NX-01

USS Jenolan's warp propulsion system display

M/ARC of the USS Jenolan

MARA access tube

Access crawlway to the M/ARA of a Constitution-class starship

Dilithium crystals

Part of the dilithium articulation frame from a M/ARA

A matter/antimatter reaction assembly (often known simply as an M/ARA) was a type of energy reactor which was fueled by injectors of matter and antimatter into a central reaction element, creating large amounts of energy when those two materials mutually annihilate each other. Matter and antimatter were injected into the M/ARA at an intermix ratio. The dilithium crystal is used to moderate this reaction. These types of powerplants were a commonly used as warp cores. (TNG: "Coming of Age")

On Constitution-class starships the dilithium crystal converter assembly was a separate unit from the intermix chamber. It consisted of the matter/antimatter integrator or reactor which channels the reactor energy to the dilithium crystal converter assembly to be energized into warp plasma for the warp engine nacelles. (TOS: "That Which Survives", "Elaan of Troyius")

The dilithium articulation frame was housed inside the M/ARA, behind the dilithium chamber hatch. (TNG: "Skin of Evil", "The Drumhead")

On monitors it was also displayed as matter/antimatter input system (ENT: "The Catwalk"), or matter/antimatter reaction chamber (TNG: "Relics")

The prototype Jem'Hadar battleship had a fatal design flaw; the braces holding together the ship's M/ARA were vulnerable to a specific type of radiation. The crew of the USS Valiant believed they could use this flaw to their advantage when they were plotting the ship's destruction in 2374. (DS9: "Valiant")

On Federation starships, this type of reactor is often used as a warp core, powering the warp drive. The most common version of this system was fueled by slush or liquified deuterium, and its antimatter counterpart, anti-deuterium. These elements were funneled through magnetic constrictors and combined within a dilithium crystal to create a stream of highly energized electro-plasma which is routed to the warp coils within the vessel's nacelles, creating a warp field. (Star Trek: The Next Generation Technical Manual)
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