The magnetic containment field, also known as a magnetic vacuum field or magnetic bottle, was a type of antimatter containment field.
A magnetic containment field was produced by the magnetic constrictor coils in the core and concentrated the antimatter to the center of the reaction chamber. It was also produced by the power transfer conduits and near the antimatter pods. The field was also utilized to propel antimatter up to the reaction chamber. If the field were to collapse or fall below 15% of its maximum integrity, the starship would be destroyed. Additionally, the magnetic field is vulnerable to quantum filaments, as they charge the vessel like a live electric wire, thus weakening the field by the inherent electromagnetic field that electricity produces. Aboard the Galaxy-class USS Enterprise-D, in the Engineering Systems Database, there was a folder titled Magnetic Containment Field Degauss Protocol. This folder contained technical manuals relevant to the topic. (TNG: "Booby Trap", okudagram; TNG: "Disaster") In 2364, a group of Bynars caused the magnetic containment field of the USS Enterprise-D to deteriorate, resulting in an evacuation of the ship. (TNG: "11001001")
On several occasions, James T. Kirk used portable magnetic vacuum field chambers to move antimatter for use as explosives. (TOS: "Obsession", "The Immunity Syndrome") On another, Scotty was able to rig a force field box to move a large chunk antimatter they acquired from the transporter to the warp core, holding the antimatter suspended in the force field apart from matter. (TAS: "One of Our Planets Is Missing")