Simultaneous in-bore rail and insulator spectra from a railgun plasma armature

Absolute spectral radiance measurements have been obtained simultaneously at the rail and insulator surfaces of a 1 cm square-bore railgun. The emission spectra were obtained through the use of quartz optical fibers which penetrated both the rail and the insulator walls. The spectral characteristics of the rail and insulator emission are quite similar, but differ significantly in magnitude. A detailed plasma radiation model was used to analyze these spectra. In order to obtain reasonable agreement between the model predictions and the experimental spectra, it was necessary to assume that there existed a broadband absorbing layer at the insulator surface. This result suggests a new physical model of the plasma armature in which insulator ablation leads to significant three-dimensional flow and affects the shape of the current emission pattern on the rail surfaces