There are two basic types of electromagnetic accelerators. A rail gun, as it is commonly called, consists of two rails with a conducting projectile that slides in between the rails completing a circuit. The current traveling through the conducting projectile causes an accelerating force known as the Lorenz Force. Rail guns are very efficient electromagnetic accelerators, but they tend to be unreliable. In order for the rail gun to be efficient, it requires several thousand volts so the large current can overcome the resistance of the circuit. Wit

Induction can be defined as "the property of a circuit containing coils to resist change in current" (Gerrish 205). In other words, circuits with coils do not like being turned on or off. The cause of this comes from the fact that it takes some time for the magnetic field to expand or collapse around a coil before the circuit reaches steady state. The geometry of the coil determines the coil's inductance. The problem with switching becomes apparent after the coil has fully energized to a stable state and then turned off. Even though there is no current flowing through the coil, there is still a lingering magnetic field surrounding it (Richards). This magnetic field induces an extremely high voltage current back onto the coil. This is known as residual induction. The current travels backwards into the switch. Since the switch only allows current to flow one direction, a voltage in the opposite direction spells death for the switch. The material composition of most semi conducting circuit components only allows one direction of current travel. The best way to solve this problem is to use a communicating diode in parallel with the coil (Barros). A diode is a semiconductor component that prohibits current flow in one direction. Any current trying to flow the opposite direction is converted into heat by the diode. It seems this problem could just be solved by changing the coil geometry to minimize inductance altogether. Strangely, inductance is a necessary evil of the coil gun.

Another aspect of gun design to consider is projectile characteristics. Materials have different magnetic permeabilities. Materials with higher permeability allow more magnetic field lines to flow through them. There is also a phenomenon called saturation. Saturation occurs when a magnetic field becomes so strong that it essentially lines up all the magnetic domains in a material. When all the domains of a material are aligned, the force of the magnetic field on the material has reached a limit. If the projectile becomes saturated, the magnetic field will not be able to put any more force on it regardless of how much the strength of the magnetic field is increased. Materials with higher magnetic permeability do not saturate as easily and therefore make more efficient projectiles. Iron is an inexpensive material that has a very high magnetic permeability (Paul). The actual shape of the projectile can also make a huge impact on how much of a force the magnetic field can put on the projectile. The actual force from the magnetic field comes from magnetic field lines that flow laterally, in the direction of desired motion, through the projectile. It makes sense that the projectile should be cylindrical instead of spherical so longer field lines can be concentrated in the projectile. Similar to the way planes experience drag from eddy currents in air, a projectile traveling through a magnetic field experiences magnetic eddy currents. These eddy currents can be reduced several ways. By cutting lateral slots in the projectile, magnetic field lines in any direction other than that of the slots are not able to travel through the projectile. Another method of reducing magnetic drag is to use a projectile made from a powdered material pressed into a form. A powdered matrix projectile eliminates all eddy currents (Paul).

Some common words found in the essay are:
Force Rail, Rectifiers SCR, Barry Closed-loop, Paul Unfortunately, Barros Decreasing, ATE Using, Six Flags, magnetic field, Propulsion Electromagnetic, coil gun, coil guns, potential energy, power supply, field lines, eddy currents, projectile coil, current flow, magnetic field lines, force magnetic field, electric potential energy, magnetic permeability, magnetic field projectile, strength magnetic field,
Approximate Word count = 2327
Approximate Pages = 9 (250 words per page double spaced)