A coilgun (also known as Gauss gun or Gauss rifle) is a type of cannon that uses a series of electromagnets to accelerate a magnetic shell to very high velocities. The appellation "Gauss gun" comes from Carl Friedrich Gauss, who formulated mathematical descriptions of the electromagnetic effect used by coilguns.
Overview
Coilguns are often mistakenly called railguns by many sources, and while they are similar in general concept (that is, a magnetic gun), they differ in operation, as a railgun accelerates projectiles down two parallel conducting rails. Coilguns are essentially identical to mass drivers, though on a smaller scale. Kristian Birkeland is commonly considered the inventor of the electromagnetic coilgun, for which he obtained a patent in 1900. The attempts to turn his invention into a usable weapon failed, and the idea was more or less forgotten for many years.
Many hobbyists use low-cost rudimentary designs to experiment with coilguns. One such design would incorporate the use of photoflash capacitors from a disposable camera as the energy source, and a low inductance coil to propel the projectile forward.
Construction
Coilguns, as the name implies, consist in a coil of wire or solenoid with a ferromagnetic projectile placed at one of its ends. A large current is pulsed through the coil and a strong magnetic field forms, pulling the projectile to the center of the coil. When the projectile nears this point, the coil is switched off and a next coil can be switched on, progressively accelerating the projectile down successive stages. In common coilgun designs, the "barrel" of the gun is made up of a track that the shell rides on, with the driver coils around the track. Power is supplied to the magnets from some sort of fast discharge storage device, typically a battery of high-capacity high voltage capacitors designed for fast energy discharge.
Operation
The power must be delivered to each successive electromagnet with precise timing, due to hysteresis. Electromagnets take some time to reach full strength after voltage is applied , so the power supply must start before the shell has reached a particular magnet. The same is true after the power is turned off, and if the shell is on the "far side" of the magnet at that time, the magnet will continue pulling on it, slowing it down. One obvious solution would be to trigger the magnets long before the shell reaches them, but because magnetic force drops off with the square of distance (that is, very quickly) too much power would be lost with such a solution. For this reason most coilguns that use more than one magnet include some sort of electronic timing device for powering the magnets, one that can be adjusted for various parameters such as power of the shot, and the mass of the shell. The gun starts with all of the magnets turned on, and then turns them off one by one before the shell reaches them. One advantage of the coilgun over the railgun is that it can be made arbitrarily long. This has a number of side effects, coilgun but the main one is that the acceleration can be much slower over a longer length, meaning that the power needed in any one section of a coilgun is much lower. However this advantage is offset by the cost and complexity of the switching system needed to supply a longer gun.
Superconducting version
A superconducting version of the coilgun is called the quench gun. Resistors attached to superconductive coils waste energy in the coil, which is turned into heat. After a time this heats the superconductor up to the point where it is no longer a superconductor, thereby coilgun construction changes its state to normal (non-superconducting). When this happens the resistance of the coil as a whole suddenly increases, dumping all of the power as heat at a very rapid rate. By carefully controlling the heating rates, the magnets can be "turned off" in sequence at the proper rates to make a coilgun, one that generates very powerful magnetic fields with high efficiency, and tends to have lower hysteresis due to the rapid dissipation of the energy in the coil.
Potential uses
Like railguns and ram accelerators, coilguns have been proposed for use in delivering payloads to space.
As a weapon, the coilgun's advantages include the fact that it has no moving parts, apart from the projectile, and the fact that the only noise heard is the movement of the projectile when it reaches very high speeds.
The University of Texas at Austin's Center for Electromechanics has been working on this [1] for years for the United States Department of Defense.
Coil guns in science fiction
Coil guns are a popular device in science fiction, especially sci-fi role playing and video games, where they go under such names as Gauss cannon or Gauss rifle (e.g., in Battletech, Syndicate, Fallout). In the miniature combat game Battletech, the Gauss Rifle is heavy projectile weapon mounted to some types of Mecha robots. The weapon causes heavy damage but produces very little heat, with heat build up being a primary concern to the efficient operation of the Mech.
In Wing Commander, the coil gun (called a "Mass Driver" in the game, even though the term mass driver implies a much larger object) is used as a primary weapon in some fighter spaceships. However, the medium range/medium damage mass driver is seldom used in later games due to the development during wartime of long-range weapons with strong firepower.
Metal Gear REX's primary offensive weapon (the rest are defensive) in the videogame Metal Gear Solid is identified as a railgun, but the description of its functionality would make it a coilgun. It is intended to launch an uninterceptable, untraceable nuclear weapon (as the coilgun would leave no propellant trail or engine flares, unlike an ICBM).
The Necrons from Warhammer 40,000 use weapons called gauss flayers to flay the skin off of their enemies. These weapons are not coilguns, however. The name is misleading.
Fallout 2 has both a Gauss rifle and a Gauss pistol as usable weapons. They are the strongest non-energy weapons in the game.
Half-Life has a usable experimental Gauss gun, or Tau cannon. This also appears in Half-Life 2, mounted on a drivable dune buggy.
Halo 2 introduces a variant of the M12LRV Warthog (the M12 LAAV) with a Gauss rifle mounted on the back, as well as the space based MAC gun (Magnetic Accelerator Cannon) seen firing in the beginning stages of the game.
StarCraft's Terran Marines each have an automatic Gauss rifle as their standard weapon.
Planetside has a weapon named Gauss rifle, which is considered a Medium Assault weapon.
Liero has a weapon named Gauss rifle and shoots a big round object at a high speed.
Master of Orion features a Gauss autocannon which would quickly fire off multiple shots.
X-COM 2 Terror from the Deep has several forms of Gauss weaponry the player can research, produce, equip, or sell.
Descent II has a weapon called a Gauss cannon. It uses the same ammo as the Vulcan cannon but does more damage.
In Andromeda, many species use Gauss guns since the knowledge coilgun physics on how to create energy weapons has disappeared.
External links
- Another Coilgun Site - Single / Multiple and portable coilguns
- JCGS - Single Stage and Multiple Stage Coilgun Development
- PowerLabs Coil Gun Page; 3 different kinds of coilguns
- Coilgun Systems
- Overview of Electromagnetic Guns
- World's Coilgun Arsenal
- Build a mini-gauss rifle with 4 magnets and a ruler, and more fun stuff.
- ForceLabs Photoflash Coilgun
Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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