Helical railgun
A railgun is in essence a single-turn motor. A multi-turn railgun would reduce the rail current and the brush current by a factor equal to the number of turns. It therefore seems worth-while to study a "helical railgun". In this hybrid device, the two rails are surrounded by a simple helical barrel, and the projectile or re-useable carrier is also helical. The projectile is energized continuously by two brushes sliding along the rails, and two or more additional brushes on the projectile serve to energize and commute several windings of the helical barrel direction in front of and/or behind the projectile. The helical railgun is in fact a cross between the railgun and the mass driver.
A helical railgun was built at MIT in 1980 and was powered by several banks of (for the time) large capacitors (circa 4 Farads). It was about 3 meters long, consisting of 2 meters of accelerating coil and 1 meter of decelerating coil. It was able to launch a glider or projectile about 500 meters.