The railgun consists of 5 major entities. The capacitor, charger, injector, barrel, and pulse capturer.
The injector simply consists of an 18 inch long 1.5 inch diameter compressed air storage tube, solenoid, and accelerator barrel. The tube takes a standard valve stem fitting, and is rated to hold 300 PSI. The solenoid is normally closed and operates at 120 VAC, it is rated at 200 PSI. The accelerator barrel holds the bullet until the solenoid dumps the air into it. The accelerator barrel is 10 inches long. The solenoid was tested at 80 PSI and fires a 10.7 gram ½” square aluminum projectile at 190 ft/s. The drag force on the projectile in the injector is approximately 12 pounds, extrapolating from what would be expected without friction at that air pressure. The injector fires the projectile into the railgun barrel.
The injector fires the projectile into the energized railgun and the projectile closes the circuit. While this is an especially easy way to switch the circuit, it is not a good way. Depending on the characteristics of the system the capacitors (or whatever pulse power system being used) could start discharging , or completely discharge before the projectile is fully inside the railgun. It is much better to switch the current with a high speed device when the projectile is in the best place in the barrel. With external switching, an injector may or may not be needed.
Another potential weakness of an injector is that it might not survive firing a projectile using a plasma armature. If the discharge is over before it has time to push the plasma out of the barrel the plasma will freely expand and may damage or blow apart the injector. So with a strong discharge plasma projectile should be avoided or the injector made robust enough to withstand very high pressures.
The simple HV railgun is exactly that, a simple high voltage railgun with only a single pair of rails. Each side of the barrel is connected the capacitors directly and the circuit is closed by the projectile. The rails are 1/8 inch steel brazed onto copper. The non-conducting barrel surface is Garolite G-10. The insulators are made of Ultra High Molecular Weight PolyEthylene (UHMW PE). The railgun is held together by 1018 Steel plates bolted together by ¼ inch grade 5 bolts. The barrel is only 8 inches long. With such a small power supply, there is really no need for a longer railgun. Both ends of the railgun are insulated with paraffin. The railgun was tested for electrical breakdown and withstood only up to 7 kV. In order to use a high voltage with this railgun an external switching mechanism is needed. If the projectile is in the barrel when the current is switched on then a much larger voltage could be used since the current is going to go through the conductive metal armature rather than through the air between the rails.
There are three, 10 kV, capacitors connected by ¼ inch aluminum bus bars. The capacitors are 198, 198, and 194 µF respectively. The capacitor bus bars bolt directly to the railgun barrel. The system stores 29500 Joules at 10 kV. The capacitors have been charged up to 10 kV and the seem to operate just fine.
The charging circuit consisted of a variable 0-130 AC transformer, a 1:120.0 transformer, and a power board to rectify the voltage. The power board is a simple half wave rectifier capable of charging a 15 kV capacitor bank at a current of 0.100 Amps.
The railgun instrumentation board was designed to measure the pulse current and voltage of the railgun during firing. Part of the board was design to measure a 0 to 4000 amp pulse in order to calibrate the Rogowski coil. The 0 to 4000 amp circuit was tested and functioned very well. Each circuit consisted of a high speed peak capture designed to function at up to 250 kHz, followed by an ADC and 3½ digit display. The peak capture consisted of an OPA627 driving a 0.001 µF capacitor through a low leakage diode. The signal held on the diode was then feed through a high precision TLC2652 Op-Amp to a simple analog to digital converter with a 3½ digit display driver for a corresponding LCD.
In most publications (about 80%) a railgun is called a railgun, the rest call it a "rail gun". I prefer the term railgun. I think of the term railgun as referring to a single unique device, and the the term "rail gun" as referring to a gun and a rail or rails. Railgun and "rail gun" are different just as darkroom and "dark room" or heavyweight and "heavy weight" refer to different things. In order to be absolutely clear and correct, and to distinguish from large cannon moved along railroads I often use the term "Electromagnetic Railgun", Railgun being the short form of "Electromagnetic Railgun".
visitors since June 10th, 2005.
