Optical Measurements in an Exploding Wire Experiment

We present optical measurements (Shadow and Schlieren pictures) of a 12.5 Joule exploding wire experiment. After performing a large number of shots some sort of time evolution can be reconstructed from the pictures. The pictures were taken during the dark phase (zero current) and the plasma phase. Although the electrical signals are quite reproducible from shot to shot (allowing a good time correlation and indicating that the global dynamics is reproducible) we observed that the individual details are quite different, probably due to the non-uniformity of the wire. We observed a uniform expansion (the volume increases almost linearly with time) with the presence of surface instabilities and there is no evident difference in the density distribution between the dark and the plasma phases. Finally, we derive a mean radius and velocity evolution with time and an approximate energy balance.