Application of High-Speed Video and Spectroscopy to Railgun Development

Abstract

High-speed video and optical spectroscopy have been used to monitor and account for the improved performance of a solid lubricating interfacial compound (SLIC) treatment of Cu armatures and Cu rails in a subsonic railgun. Videos were taken at 68k frames per second both down bore (breech view) and along the exit path of the gun (muzzle view). A spectrometer collected data at 1 spectrum per ms outside the muzzle. Armatures were made by threading Cu or Cu-clad Al staples through a Delrin projectile. The SLIC treatment consisted of rubbing staples and rails with a fiberglass-reinforced PTFE (Rulon). Untreated staples and rails were susceptible to both arcing and subsequent light emissions, with light emission lasting much longer than coincident voltage spikes in muzzle voltage traces. SLIC-treated staples and rails showed significantly less light emissions, which allowed for real time, laser spot tracking of projectile motion. Image analysis showed that projectiles were accelerated at 10–14 kGees within 1 ms to final speeds around 130 ± 10 m/s. These speeds were consistent with exit speeds measured by a dual laser-beam speed detector. Cu staples exited the muzzle with only a small amount of light emission, whereas Al and Cu-clad Al staples produced an extended trail of light. Spectroscopic analysis identified atomic and ionic excitations of Cu and later molecular CuO with both Cu and Cu-clad Al staples. Molecular H2 lines were also detected, suggesting burning of Delrin. Spectroscopy identified the extended trail from Cu-clad Al staples to be AlO vapors from molten Al particles.