Measurement & simulation of backscattered electrons from a strip electron beam source

During electron beam processing, a fraction of the incident power gets back scattered from the target surface, which can be as high as 40% of the incid ent beam power depending on the beam energy and atomic number of the target material. In the case of a strip electron gun, a uniform magnetic field is used for focusing and deflection of electron beam through 270 degrees. Wit h the strip beam (78 mm x 5 mm, 36 kW), experimental results of the 2-D dis tribution of the backscattered electron current from copper target in its p lane, parallel and perpendicular to the focal strip are presented. These re sults are compared with calculated data using reported energy distribution of backscattered electrons (E.H.Darlington, J. Phys. 8 (1975) 85). The inte grated heat flux associated with backscattered electron is experimentally m easured and compared with calculated values for incident power of 86 kW. Wi th 12.25 kW/cm(2) of incident strip beam power, the back reflected electron peak power density was observed to be 59W/cm(2). This power density will b e higher for high incident power densities and for targets of high atomic n umbers and dan be used in precoating treatments of substrate such as outgas sing and cleaning, keeping it at elevated temperature during continuous coa ting process, and also for outgassing, cleaning and sharing heat load requi red for pre-melting of the feeder material during melting and casting. (C) 2001 Elsevier Science Ltd. All rights reserved.