1 MA Breech Upgrade for the U.S. Army Research Laboratory's (ARL's) Rectangular 22- x-44-mm In-bore Cross Section Railgun

The 4.5-MJ capacitor-based power supply at the U.S. Army Research Laboratory (ARL) originally contained 18 modules at 250 KJ each. Within each module, five 840-microF Aerovox capacitors and either a 60-microH or a 30-microH inductor, allowed the generation of output pulses of different profiles. Since 2001, the power supply, railgun and breech, has performed safely and reliably for over 500 single shot launches. During 2007, all capacitors were replaced with new 950-microF General Atomics capacitors, increasing the total energy of the system to 5.2 MJ. During 2009 a study was started to assess the feasibility of modifying the existing breech that would result in a breech of smaller size, improved means to load projectiles, and capable of firing multiple shots at 1 MA. A first analysis focused on improving the uniformity of current distributions at the breech-insert-rail interfaces, suspected in causing of some catastrophic failures seen previously during multi-shot launches. Next, the breech contact forces were characterized as well as selection of improved materials and geometries for the breech plates and rail inserts. This report includes progress made until the facility was shutdown in November 2009 and contains general conclusions to facilitate the implementation of a multi-shot 1-MA breech. The original document contains color images.