Magnetic constrictor
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Magnetic constrictors are specialized variants of plasma conduits that are used on warp cores, impulse thrusters and deflector dishes of Federation starships. They shrink to apply huge pressure to particles caught within the field, this allows particles to be fired out of small holes or weak points in the containment field. In a starship's warp core, antimatter particles are fired into the matter-antimatter reaction assembly using a magnetic constrictor.
In 2371, when the USS Voyager was pulled into the Delta Quadrant by the Caretaker, Captain Janeway ordered that the magnetic constrictors be locked down, in order to avert a warp core breach. (VOY: "Caretaker")
In 2372, B'Elanna Torres destroyed the self-guided missile Dreadnought by burning through the magnetic constrictor casing of its warp core with her phaser. (VOY: "Dreadnought")
In 2373, Chief O'Brien claimed he wanted to test new magnetic constrictors on a runabout's impulse thrusters, really only intending to pilot that runabout to the mouth of the Bajoran wormhole. (DS9: "The Assignment")