OBSERVATION OF SOLID ARMATURE BEHAVIOR

High efficiency railgun armatures require metal-on-metal sliding of ar mature on rail without arcing. A succession of armatures has been cons tructed and tested in a 25 mm square bore railgun. The first armature tested was a single leaf copper staple having 12 fingers per side, of the type pioneered in the Canberra railgun. At moderate currents (250 kA) the staple armature performed well, but at higher currents transit ion to arcing contacts occurred as current was falling. The effects of modifying rail surfaces was also tested, including the use of transve rse mini-grooves to enable friction to be calculated, angled lands to improve armature contact, and insulating inserts to trip transition. T his led to a design in which a polycarbonate ''spring'' was used to ca rry 11 wires, 2 mm in diameter. This armature, when using copper wires , carried 360 kA without premature transition. Various other designs h ave also been tested, including monolithic aluminum alloy armatures, w hich successfully carried currents of 600 kA.