Optical diagnostics of railgun plasma armatures

A 1-cm square-bore railgun facility, dedicated to the development of diagnostic techniques and the study of plasma armatures, has been put into operation. Time-resolved, in-bore optical measurements of laser transmission and plasma spectral emission have been obtained, together with B-dot probe and piezoelectric pressure measurements. These measurements provide a means to determine the spatial profiles of armature current, pressure, and plasma emission relative to the measured projectile position and velocity. A novel method was used to deconvolve the signal from B-dot probes to obtain the current density in the arc without recourse to a priori assumptions for the mathematical form of current profiles. It was observed that plasma emission passes through a minimum near the armature current maximum, and it is suggested that insulator ablation products in the boundary layer may play a significant role in the wall radiative transfer. High-resolution, time-integrated spectra from the bore interior revealed that resonant absorption lines constitute the only significant spectral features, and that copper and aluminium each constitute approximately 10% of the armature material.<
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