Intermix chamber

The intermix chamber is a major component of a starship's warp core. Its functions include the maintenance and regulation of plasma pressure within the core.

While assisting Zefram Cochrane in 2063, Geordi La Forge could recall the intermix chamber of the Phoenix from memory. 

In November 2154, tampering by a group of Klingons caused a malfunction in the intermix chamber aboard the. As a result, plasma pressure within the chamber began to rise, threatening to destroy the ship. In order to reduce the pressure, Enterprise had to maintain high warp until the damage could be repaired. 

In 2370, while posing as a thief named Galen, Captain Jean-Luc Picard manufactured an intermix chamber malfunction on board Arctus Baran's mercenary vessel, causing the ship to accelerate out of control and the plasma pressure to increase. 

Background
In a filmed but deleted scene in, Wesley Crusher mentions that the USS Titan is equipped with a double refracting warp core matrix with twin intermix chambers.

In Mr. Scott's Guide to the Enterprise, the function of the intermix chamber of a refit is explained in detail. Both matter and antimatter flow simultaneously inside the intermix chamber. The chamber is divided into a vertical and a horizontal chamber that join together in main engineering. The horizontal chamber branches out to the nacelles and also powers all of the phaser banks. The vertical chamber is connected at the upper end to the impulse deflection crystal, that normally powers the impulse drive. At the bottom of the vertical chamber are the matter and antimatter tanks from which the reactants are drawn. There are several energy converters connected to the vertical chamber that provide plasma for the more basic ship functions not related to propulsion.