A particle-beam weapon uses a high-energy beam of atomic or subatomic particles to damage the target by disrupting its atomic and/or molecular structure. A particle-beam weapon is a type of directed-energy weapon, which directs energy in a particular and focused direction using particles with negligible mass. Some particle-beam weapons are real and have potential practical applications, e.g. as an antiballistic missile defense system for the United States and its Strategic Defense Initiative. The vast majority, however, are science fiction and are among the most common weapon types of the genre. They have been known by myriad names: phasers, particle accelerator guns, ion cannons, proton beams, lightning rays, rayguns etc.