Railguns from the late 1800s to 1980

    Although theory had existed since the nineteenth century, no major development occurred until the middle of the twentieth century. Earlier attempts had been reported, one Mr. Benningfield put an advertisement in 1844 in which his "SIVA" or the DESTROYER promised to revolutionize the battlefield. This is surprising as it occurred well before the 1878 date of Lorentz's theories. Either way, Benningfield's promised revolution never happened, and nothing is known of what happened to Benningfield or his electric gun.


Benningfield's Electric gun SIVA as shown in 1844 Advetisement (Image from IEEE Transactions on Magnetics)

    In 1944, using batteries as his power source, Joachim Hänsler created the first working railgun, which was able to propel a 10 g mass to speeds of about 1km/s. Although certainly impressive, the achieved speeds were no more remarkable than those of the chemical propellants of the time. The relatively slow speed of Hänsler's railgun can be traced to the type of material that he had used in the projectile.  In his trials, he used a metallic conductor as the armature this presented two major problems. The first was that as the armature was a solid, it was impossible to ensure that the armature constantly maintained contact with both rails.  The dynamics of the projectile's motion meant that at times the armature lost contact, stopping the flow of the circuit and hence losing the acceleration during that time. The only way that the armature could be made to maintain contact with both rails would be to use brushes or some other contact device, all of which would have created an unacceptable increase in friction. The second problem with solid armatures was that at high speeds they tended to melt, resulting in a rather messy gunk at the muzzle. This was a major problem even when graphite was used as a lubricant, the high temperatures created in fast moving railguns would rapidly evaporate the graphite.
    In addition, a large erosive drag force existed in normal operations, this led to increased wear and tear on the rails, so much so that they were required to be replaced every few trials, a very expensive prospect. This in combination with the rather low velocities achieved made railguns more science fantasy than reality until 1964 when the age of railguns truly began.
    That year, MB Associates used a 28kJ Capacitor to accelerate 5 and 31 mg nylon cubes with a plasma arc as the armature. In this process, a fuse placed behind the projectile (nylon cube) is used to initially complete the circuit. As the current ran through the fuse it vaporized the metal and established the initial plasma arc. The plasma arc is moved forward by Lorentz's Force, and pushes the nylon cube forward along with it. The plasma arc is confined behind the nylon cube by a dielectric container enveloping the entire setup  (Fig.2).


Railgun cross-section

    Using plasma arcs over solid metallic armatures eliminated the problems that had previously limited railgun velocities to 1-3 km per second, consequently muzzle velocities of 5-6 km/s were achieved. Later, in 1972 researchers at the Australian National University were able to accelerate 3 g projectiles to similar speeds using plasma arcs and a 900kJ homopolar generator. The efficiency of these railguns in converting electrical energy to kinetic were less than 5%, even when the loss of energy into the circuit had been subtracted away from the total energy. A far cry, from the near 99% efficiency rate of modern day "magneto launchers" Yet, the biggest problem these railguns faced was that beyond speeds of around 5 km/s, researchers found that the rails were so superheated that their surfaces evaporated. This was not a problem in itself, all that was required was that the rails be replaced more often. However, the evaporated metal formed plasma, which in turn led to secondary arcs that diverted current away from the armature plasma arc. Moreover, there was also another source of secondary arcs. Typically, some plasma from the armature staggers along behind the main body of plasma. Under low velocities, the amount of this plasma is not sufficient to form another arc. However, at higher velocities, increased amounts of plasma were left in the trail, and consequently secondary arc formation occurred.