A railgun uses the flow of electricity to accelerate a projectile to
incredibly high velocities. It is distinct from other guns (or more
correctly, cannons) by the fact that no chemical combustion is necessary. In
fact, no gasses are used to accelerate the projectile. All the acceleration
is done by the flow of electricity.
Railguns are a relatively new technology and are much less efficient than
other chemical means. Railguns that operate with a total efficiency of over
two percent are considered highly efficient. The advantage of railguns is
that they can accelerate a projectile much faster than is possible using any
other means. To date, railguns can easily fire a projectile at over
velocities of 10 kilometers per second. Velocities of approximately 150
kilometers per second are considered possible. By comparison, the maximum
velocity that a light gas gun has fired a projectile is less than eight
kilometers per second.
HOW THEY WORK
A railgun is essentially a linear DC motor. Instead of the current spinning
an armature, the current pushes a projectile (see Figure below). A railgun
consists of two parallel field-producing metal plates, the distance between
them being the diameter of the projectile. A high-current DC source of
electricity is discharged through the projectile via the two plates. This
creates a force known as the Lorentz force that is perpendicular to the
flow of the current. This propels the projectile in the opposite direction
that the current came from.
