Target surface layer dynamics during application of intense electron beams

Summary form only given. Intense pulsed electron beams are commonly used to improve mechanical properties of metal targets in near-surface regions or for surface alloying. In some cases, however, the intended property changes are accompanied by the development of surface roughness. The exact origin of this phenomenon is still under debate. In this work, the dynamics of the target surface layer in its melted stage is investigated experimentally and theoretically. The pulsed electron beam facility GESA at KIT is used to generate electron beams with power density 0.5-2 MW/cm2, electron energy 120 keV, and pulse duration up to 200 μs. Various fast in-situ optical diagnostic tools have been set up and successfully tested during treatment of stainless steel, copper, and aluminum targets. After this preceding work, a systematic investigation of the influence of various materials and of specific beam parameters on the surface layer dynamics is now performed. The experimental studies are accompanied by numerical simulations of heat transfer and melt motion and by theoretical considerations concerning the relevance of possible hydrodynamic instabilities.