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 miniscule mass. Some particle-beam weapons have potential practical applications, e.g. as an antiballistic missile defense system for the United States and its cancelled 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.
The concept of particle-beam weapons comes from sound scientific principles and experiments currently underway around the world. One effective process to cause damage to or destroy a target is to simply overheat it until it is no longer operational. However, after decades of R&D, particle-beam weapons are still very much at the research stage and it remains to be seen if or when they will be deployed as practical, high-performance military weapons.
Particle accelerators are a well-developed technology used in scientific research for decades. They use electromagnetic fields to accelerate and direct charged particles along a predetermined path, and electrostatic "lenses" to focus these streams for collisions. The cathode ray tube in many twentieth-century televisions and computer monitors is a very simple type of particle accelerator. More powerful versions include synchrotrons and cyclotrons used in nuclear research. A particle-beam weapon is a weaponized version of this technology. It accelerates charged particles (in most cases electrons, positrons, protons, or ionized atoms, but very advanced versions can accelerate other particles such as mercury nuclei to near-light speed and then shoots them at a target. These particles have tremendous kinetic energy which they impart to matter in the target's surface, inducing near-instantaneous and catastrophic superheating.
Charged particle beams diverge rapidly due to mutual repulsion, so neutral particle beams are more commonly proposed. A neutral-particle-beam weapon ionizes atoms by either stripping an electron off of each atom, or by allowing each atom to capture an extra electron. The charged particles are then accelerated, and neutralized again by adding or removing electrons afterwards.
Cyclotron particle accelerators, linear particle accelerators, and Synchrotron particle accelerators can accelerate positively charged hydrogen ions until their velocity approaches the speed of light, and each individual ion has a kinetic energy range of 100 MeV to 1000 MeV or more. Then the resulting high energy protons can capture electrons from electron emitter electrodes, and be thus electrically neutralized. This creates an electrically neutral beam of high energy hydrogen atoms, that can proceed in a straight line at near the speed of light to smash into its target and damage it.
The pulsed particle beam emitted by such a weapon may contain 1 gigajoule of kinetic energy or more. The speed of a beam approaching that of light (299,792,458 m/s in a vacuum) in combination with the energy created by the weapon would negate any realistic means of defending a target against the beam. Target hardening through shielding or materials selection would be impractical or ineffective, especially if the beam could be maintained at full power and precisely focused on the target.
The U.S. Defense Strategic Defense Initiative put into development the technology of a neutral particle beam to be used as a weapon in outer space. Neutral beam accelerator technology was developed at Los Alamos National Laboratory. As part of the Beam Experiments Aboard Rocket (BEAR) project, a prototype hydrogen beam weapon was launched from White Sands Missile Range in July 1989 and successfully deployed into Low Earth Orbit. It was operated successfully in space and after reentry was recovered intact. In 2006, the weapon prototype was transferred from Los Alamos to the Smithsonian Air and Space Museum in Washington, DC.