Delay in plasma generation on copper and duralumin conductors coated with titanium or zirconium

Abstract

Skin explosion investigations have been performed for homogeneous and double-layer cylindrical conductors made of copper and duralumin and coated with titanium or zirconium. Titanium and zirconium have close values of electrical conductivity and sublimation energy density, whereas the ionic mass of zirconium is twice that of titanium. The experiment was carried out on the MIG high current generator at a current of amplitude up to 2.5 MA and rise time 100 ns. The plasma generated on the conductor surface was imaged using a four-frame optical camera with a frame exposure time of 3 ns. The internal structure of the surface plasma was examined using transmission images of the plasma exposed during 2-3 ns to the x radiation with hv>0.8 keV generated by an X-pinch. It has been demonstrated that the time delay to the plasma formation on the surface of double-layer copper and duralumin conductors with a deposited zirconium or titanium layer is comparable for Zr and Ti (with the conductivity ratio equal to 26-27 for a homogeneous copper conductor and a deposited layer and to 8.2-8.5 for a homogeneous duralumin conductor and a deposited layer), and it is shorter for double-layer duralumin conductors than for double-layer copper conductors. In a magnetic field lower than 300 T, plasma formation on the surface of a double-layer copper conductor started about 400 ns later than on the surface of a homogeneous copper conductor and 250 ns later than on the surface of a duralumin conductor. When the field was increased to 350-400 T, the delay time to plasma formation decreased to about 35 ns. For double-layer conductors, the difference in expansion velocities between titanium and zirconium surface plasmas was insignificant.