Ion emission from solid surfaces induced by intense electron beam impact

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Abstract
Ions or ionized neutrals released from solid surfaces by electron beam impact can be accelerated and trapped in the beam potential causing beam disruption. Experiments have been performed on the DARHT-I accelerator (1.7 kA, 19.8 MeV, 60 ns) to study this phenomenon. The beam, focused to a range of diameters, was transmitted through thin targets made of various materials. The time evolution of the beam radial profile was measured downstream of the target. For low current density, the downstream-beam radial profile was time invariant as expected for a pure electron beam. At higher current density, the downstream beam was clearly disrupted during the pulse followed by a large-amplitude transverse centroid instability. Two-dimensional calculations using the Lsp particle-in-cell code show that if the space-charge-limiting ion current is allowed to flow after the target surface temperature increases by about 400 K, the main features of the experimental observations are replicated. Three-dimensional Lsp calculations show growth of the ion hose instability at a frequency close to that observed in the experiments.