Characterization of high-current electron beam interaction with metal targets.

The process of electron beam interaction with metal targets was characterized using electrical and optical diagnostics. Electron beams with current density of 5-10 A/cm2, electron energy up to 120 keV, pulse duration up to 200 μs, and cross-sectional area of 8-30 cm2 at the target surface were generated by GESA I and GESA II facilities. Streak imaging of the target surface specular reflectivity was used to determine the onset of melting and re-solidification of the target surface. Using time- and space-resolved schlieren imaging, the evolution of surface irregularities was studied. Experimental and numerical investigations of the neutral flow evaporated from the target surface showed a neutral density of ∼1019 cm-3 in the vicinity of the target and neutral velocities up to 2 × 105 cm/s. Framing and streak images of visible light emission were used to study the temporal evolution of the target surface plasma and vapors. Time- and space-resolved spectroscopy was applied to determine the surface plasma density and temperature, which were found to be ∼1014 cm-3 and ≤1 eV, respectively. Because of this small plasma density, electric fields in the plasma sheath are not sufficient to cause electrohydrodynamic instability of the liquid target surface. However, hydrodynamic instabilities due to the intense neutral flow observed in experimental and numerical studies are likely to be responsible for the growth of wavelike irregularities. [ABSTRACT FROM AUTHOR]