Coilgun

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.

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.

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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 offset by the cost and complexity of the switching system needed to supply a longer gun.

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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.

Related Topics:
Superconducting - Resistor

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