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A plasma weapon is any theoretical firearm designed to use plasma (high-energy ionized gas) as a weapon. The plasma is typically intended to be created by superheating lasers or superfrequency devices.
Such weapons can be intended to be lethal, causing death by serious burns or the melting of targets, or non-lethal and intended to disrupt electronics using an electromagnetic pulse.
Current research 
Boeing has considered furthering the research of plasma weapons and directed energy weapons, or DEW. Boeing Phantom Works has several ideas, one of which is that a plasma weapon aboard a hypersonic aircraft could possibly skim off the plasma that naturally forms around the airframe of a vehicle traveling at Mach eight. They hypothesize that this captured plasma could then be redirected by a focusing system and used as a weapon. There is an apparent interest in plasma for aerospace technologies in the U.S.
A nonlethal weapon designed to use a laser to induce a high energy state in gases is currently being funded by the United States military. The leading tip of the incoming beam ionized the target material, while the remainder is absorbed by this newly created plasma causing it to expand rapidly. This rapid expansion not only has an effect similar to a flash-bang grenade, but also creates an extremely strong EM field which is tunable through the output of the laser itself. This EM field stimulates nerves throughout the body triggering muscle paralysis and/or intense sensations of pain. There have been concerns that the technology may be unethically used, as it is possible to stimulate pain nerves throughout a person's body creating unimaginable levels of agony.
With the assistance of a $2.7 Million U.S. contract, Stellar Photonics is developing a Plasma Acoustic Shield System, or PASS. The PASS uses a high-energy laser to create an airborne ball of plasma, then uses another laser to create a shock wave inside the plasma ball, creating a flash of light and explosion.
A censored twelve-page contract between the U.S. Navy and the Univ. of Florida to "study the consequences of using an electromagnetic pulse emitted by laser induced plasma channels" on humans. The contract states that several directed energy weapons can be used alone or with each other to induce non-lethal to lethal attacks.
Practicality of plasma weapons 
At present, plasma weapons are merely theoretical, as currently they need more power than any handheld device could supply. If small portable fusion reactors are made, one potential source of weapons-grade plasma sources might be a direct tap on a fusion reactor, especially a dense plasma focus, since the natural yield of such a reactor is a hot high-speed plasma beam. Making real plasma weapons will need a major scientific breakthrough, as the concept of plasma-firing weapons is scientifically difficult, for various reasons:
- The technology to create plasma compact toroids and particle beams is presently far too bulky for anything man-portable. In such a high-performance design, the plasma would have to be stored and created in highly focused magnetic bottles, such as those used in NASA's VASIMR rocket: this design has been suggested as a potential weapon design for future real human-engineered plasma weapons. For simpler designs based on plasma cutting torches, a designer might be able to heat the plasma with an arcjet, if his power source is strong enough.
- Using current technology, if a plasma beam was fired in a planetary atmosphere, it would quickly be stopped by atmospheric resistance and would make a short hot flame like a blow torch.
- The plasma shot out of a plasma weapon would tend to dissipate in the surrounding environment within about 50 centimeters from the gun, from thermal and/or electric pressure expansion, called blooming, unless:
- The magnetic confinement bottle is extended all the way to the target. Modifications to this bottle could make the plasma home in on its target. On the other hand, magnetic fields of such strength could also be used to block the plasma.
- The plasma is somehow made self-sustaining over a much longer time period (as with ball lightning).
- The particles are fired fast enough to reach a target before blooming occurs. This is then a particle beam more than a plasma shot (at least as much as any technical definition for such weapons exists). This would work for use outside atmosphere (i.e. in a space vacuum), but within an atmosphere would merely cause a hotter short flame from more violent collision between the flying particles and the atmosphere.
- It might also be possible to generate a laser beam "tunnel". High-energy lasers ionize the air around the beam, heating the atmosphere and providing the plasma bolt with an easy passage to the target (see electrolaser).
- Another laser-assisted plasma weapon approach for use in atmosphere is possible if the laser is powerful enough to blast the air out of the way, but having the plasma particles reach the target before the newly-created vacuum channel collapses in on itself is a problem unless the weapon possesses sufficient power to either sustain the channel or the aforementioned "plasma particle beam" approach is used.
- It may also be possible to encase a bolt of plasma in a capsule of some material, possibly a polymer. This would allow the plasma to reach a medium distance before the capsule wears out. However, such a material could also be used to block the plasma.
- A plasma round would glow very brightly due to blackbody radiation, leading to quick substantial energy loss. This might also represent a blinding hazard for the operator and bystanders. From basic physics, a 1 cm ball of plasma at 10,000 Kelvin (K) would be equal to a 180 kilowatt (kW) bulb.
- Many materials already exist that are highly resistant to plasma, reinforced carbon-carbon used on the Space Shuttle's nose cone for example; or the ceramic inserts used in bulletproof vests.
Plasma weapons in popular media 
Plasma weapons were first suggested in science fiction, and have become a popular fictional weapon.
See also 
- new scientist: http://www.newscientist.com/article.ns?id=dn7077
- "Plasma Shield may stun and disorientate enemies". New Scientist. Retrieved 2008-09-22.
- P.J. Turchi and W.L. Baker, Generation of high-energy plasmas by electromagnetic implosion, J. Appl.Phys., Vol. 44, 11, (1973).