Railgun Basics

A Railgun, also known as a “Schienenkanone” in German, is similar to a Coilgun but relies on entirely different magnetic forces.

While in a Coilgun, ferromagnetism is the driving force, the Railgun’s operation is mainly based on the Lorentz force, specifically the Lorentz force acting on a current-carrying conductor.

The Lorentz force is determined by the following parameters:

1. The current flowing through the conductor (I in Amperes)
2. The length of the conductor (L in meters)
3. The strength of the magnetic field (B in Teslas)

The relationship between these parameters is given by the formula F = I x B x L, where:

• F ⇒ The force in Newtons
• I ⇒ The current in Amperes
• B ⇒ The magnetic field in Teslas
• L ⇒ The length of the conductor in meters

The “x” here represents the vector cross-product, but in practice, we can also write the formula as F = I * B * L.

The sled should preferably be made of a non-ferromagnetic material, not iron, nickel, or similar materials. Materials like copper or aluminum are usually the best choices.

Let’s first consider the flow of current. In our illustration (see Fig. 1), the orange bars represent our rails, both connected to a power source. Our movable sled (shown in gray) connects the rails, completing the electrical circuit, which results in a current flow indicated by the blue arrows.

Back to the formula: The length L corresponds to the distance between the two rails or the width of the sled. The current I represents the current flowing from one rail to the other (via the sled).

Now, when a magnetic field (B) acts perpendicular to the rails, the sled is pushed out of the rails.

The question is, where does this magnetic field come from? Normally, this field is not generated externally by magnets or electromagnets. Instead, it is created by the current flow itself, which generates a magnetic field around its conductor (red arrows). Within the rails, this field is nearly homogeneous, and this field is our B. So, we have all the necessary quantities together.

Here’s another isometric representation of the process: Current (blue) flows through the rails (orange) via the sled (gray). The current flow creates a magnetic field (red), exerting a force on the current-carrying sled and moving it out of the rails (green).