Interaction of an intense relativistic electron beam with preformed channels

The authors report the interaction of an intense relativistic electron beam (REB) with preformed channels in gaseous atmospheres demonstrating the effects of reduced density, avalanche ionization, pre existing conductivity, and channel currents. The intense REB was produced from a field emission diode driven by the 1 MV pulse from a folded Blumlein pulse forming line. The cathode was graphite and the anode was titanium foil, ≅ 0.038 mm thick. The REB emerging from the anode foil contained ≅ 16 kA within the foil diameter of 10.4 cm and ≅ 2.5 kA through a central aperture of diameter 1.5 cm. Its time history was approximately a half sinewave with peak current 16kA and period 80 ns. Channels in the atmosphere were created using laser guided electric discharges in which the beam from a Q-switched Nd:glass laser induced air breakdown off aerosols and these plasmas guided the electric discharge (≅ 250 kV, ≅ 1000 J, period ≅ 3 μs, peak current ≅ 10 kA). At early times the channel was highly conducting (≅ 44 S/m) with radius ≅ 1 cm. Later the channel cooled becoming effectively non-conducting when the radius was ≅ 1.5 cm