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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 annihilated each other. Matter and antimatter were injected into the M/ARA in an intermix ratio. The dilithium crystal is used to moderate this reaction. These types of power plants were 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 channeled 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 the matter/antimatter input system, (ENT: "The Catwalk"), the matter/antimatter reaction chamber (TNG: "Relics") or the matter/antimatter reaction system. (PIC: "Dominion")

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")

In 2368, after the computer systems of the Enterprise-D were disrupted by a energy wave from a Satarran starship, Geordi La Forge accessed the basic system directories of the engineering department. According to the department, the matter-antimatter reaction assembly was off-line. (TNG: "Conundrum")

On Federation starships, this type of reactor was often used as a warp core powering the warp drive. The most common version of this system was fueled by slush or liquefied 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 was routed to the warp coils within the vessel's nacelles, creating a warp field. (Star Trek: The Next Generation Technical Manual)