Coilgun

Encyclopedia : C : CO : COI : Coilgun

A coilgun (also known as Gauss gun, Gauss cannon or Gauss rifle) is a type of cannon that uses a series of electromagnets to accelerate a magnetic shell to very high velocities. The name "Gauss gun" comes from Carl Friedrich Gauss, who formulated mathematical descriptions of the electromagnetic effect used by coilguns.

Contents

1 Overview
2 Construction
3 Operation

3.1 Superconducting version

4 Potential uses
5 Coilguns in science fiction
6 See also
7 External links

Overview

Coilguns are often mistakenly called railguns, 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

A coilgun, as the name implies, consists of 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 to pull 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, 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 partially 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 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. Though coilguns have been shown to reach supersonic speeds, they are far less capable than railguns.

The University of Texas at Austin [Center for Electromechanics] has been working on this [link] for years for the United States Department of Defense.

A superconducting quench gun could be created by successively quenching a line of adjacent coaxial superconducting coils forming a gun barrel, generating a wave of magnetic field gradient travelling at any desired speed. A travelling superconducting coil can be made to ride this wave like a surfboard. The device in fact represents a mass driver or linear synchronous motor in which the propulsion energy is stored directly in the drive coils.

Coilguns in science fiction

Coilguns 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, Crimsonland, StarCraft, Ogame, Half-Life, Descent, Mechwarrior series, Halo 2, Cyberstorm 2, ''Metal Gear Solid, OGame MechCommander, and Battlemech). Gaussguns have also appeared in The Night's Dawn Trilogy.

External links

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.