Railgun Theory

A Railgun's effect is caused by a force known in physics as the Lorentz force.  In simple terms, when current (electron flow) is moving in opposite directions in two wires running parallel, they will repel each other.  If the current flow in the wires is in the same direction they will attract. The force is the effect of electromagnetic fields caused by electron movement.  The higher the current, the stronger the force.

A Railgun has two rails that run parallel to each other. An armature sits between them completing the path of current.  The rails and armature are all producing Lorentz force's and are repelling each other.  the rails are repelling each other and each rail is repelling the armature.  The rails are fixed in position and the armature is allowed to move.  The repelling forces cause the armature to move away from the rails and out the end of the Railgun.

In most Railgun setups, the force applied to splitting rails apart is >10 times the force pushing the armature.  The current flow in the rails is 180˚ from each other, exact opposites so they create the most repulsion. The current path through the armature is 90˚ from either of the rails so it is much less. 

Since the armature feels very little of the force, a Railgun is very inefficient.  A well tuned Railgun might reach 10% efficiency, meaning 10% of the energy used by the Railgun is given to the armature.  The other 90% try's to tear the rail apart.

A Joule is a measure of raw energy. A 357 Magnum has a muzzle energy of around 750J (Joules). So for a (perfect) Railgun to put the same amount of energy into the armature it would use >7500J.

The math that describes the forces at work in a railgun is complicated.  The calculus describes how every infinitesimally small point in the rail and armature are effected by every other infinitesimally small point.  For an in depth explanation see: http://www.eng.auburn.edu/department/ece/railgun/theory.htm

Wikipedia Also has a great explanation of it here: http://en.wikipedia.org/wiki/Railgun

Page last updated: 06/11/2005 10:04 AM