A coil gun (or Gauss gun) is an electromagnetic launcher that offers a few advantages over rail guns. The "barrel" of a coil gun is a series of copper coils. These coils are energized sequentially, setting up a traveling magnetic field on the inside of the barrel. This magnetic field attracts a ferromagnetic projectile down the barrel. Since the projectile of a coilgun floats in the barrel and never touches the coils, it suffers less wear and tear, and these guns are completely quiet. Coil guns have been demonstrated to supersonic velocities, but they are not as efficient or as capable as railguns.
Problems with Rail Guns
In theory, rail guns are the perfect solution for short- and long-range firepower. In reality, they present several serious problems:
- Power supply:Generating the power necessary to accelerate rail gun projectiles is a real challenge. Capacitors must store electric charge until a sufficiently large current can be accumulated. While capacitors can be small for some applications, the capacitors found in rail guns are many cubic meters in size.
- Resistive heating: When an electric current passes through a conductor, it meets resistence in the conductive material -- in this case, the rails. The current excites the rail's molecules, causing them to heat. In rail guns, this effect results in intense heat.
- Melting: The high velocity of the armature and the heat caused by resistive heating damages the surface of the rails.
- Repulsion: The current in each rail of a rail gun runs in opposite directions. This creates a repulsive force, proportional to the current, that attempts to push the rails apart. Because the currents in a rail gun are so large, the repulsion between the two rails is significant. Wear and tear on rail guns is a serious problem. Many break after a few uses, and sometimes they can only be used once.