Delay in plasma generation on the surface of coper and duralumin conductors coated with dielectrics

The skin explosion was investigated for homogeneous and double-layer cylindrical copper and duralumin conductors coated with zirconium dioxide. The MIG generator used in the experiment produced a current of amplitude up to 2.5 MA and rise time 100 ns. To detect the plasma generated on the surface of a conductor due to its electrical explosion, the light emitted by the plasma was imaged using a four-frame optical camera with a frame exposure time of 3 ns. In addition, vacuum x–ray diodes were used to detect the instant at which the temperature of the surface plasma, assumed to be a blackbody, became greater than 1 eV. The internal structure and density of the surface plasma were examined based on its transmission images. The images were taken by exposing the plasma to the x-radiation with h ν > 1 keV generated by an X-pinch for 2–3 ns. The QUINTA facility was used to carry out plasma-assisted deposition of multilayer coatings composed of alternating 0.8-μm-thick zirconium dioxide layers and (more durable) 0.2-μm-thick zirconium layers. The total number of layers in a coating could be up to sixteen. At magnetic fields lower than 300 T, the onset of plasma generation on the dielectric-coated load part occurred with a delay of up to 70 ns relative to that on a bare copper or duralumin conductor. Increasing the field to 350–400 T decreased the delay in plasma generation to about 30 ns.