A thoron shock emitter was a weapon of Cardassian design. The Cardassian tactical missile ATR-4107, later known as Dreadnought, was equipped with a thoron shock emitter as part of its defensive systems.
In 2372, B'Elanna Torres identified the thoron shock emitter as the only possible weakness in the missile's defenses, since when it fires at full power it destabilizes the reactor core for thirty seconds. The USS Voyager attempted to take advantage of this by firing a tachyon beam at the core after the emitter discharged in the hopes of overloading the core, but Dreadnought was able to send a plasma burst back along the beam, resulting in heavy damage to Voyager. (VOY: "Dreadnought")