Mass Density Distribution in the Surface Plasma of a Cylindrical Conductor during a Skin Explosion

The process of surface plasma formation during a skin explosion of cylindrical duralumin conductors in fast rising magnetic fields was investigated experimentally. The experiments were performed on a MIG high-current generator at currents of amplitude up to 2.5 MA and rise time 100 ns. The plasma formed at the conductor surface was detected by its luminescence in the visible range using a four-frame optical camera with an exposure time of 3 ns. In addition, vacuum x-ray diodes were used to detect the instant the surface plasma reached a temperature above 1 eV in the black body approximation. The internal structure of the surface plasma and its mass density were investigated using shadowgraphs that were obtained with an exposure time of 2-3 ns by irradiating the plasma with the x rays of photon energy hv > 0.8 keV generated by an X-pinch. Comparison of the probe radiation densitograms between the plasma column and step filters has shown that the line-of-sight linear mass of the column was greater than that of a 20 μm-thick Al foil. In this case, the linear mass of the surface layers at a radius of 1.6-1.7 mm corresponded to that of a 10 μm-thick foil and rapidly decreased with increasing radius. The mass density at the boundary of the plasma column at the time of radiographs was estimated to make 8-12% of the solid state density.