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

Abstract

During electron beam processing, a fraction of the incident power gets backscattered from the target surface, which can be as high as 40% of the incident 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°. With the strip beam (78 mm×5 mm, 36 kW), experimental results of the 2-D distribution of the backscattered electron current from copper target in its plane, parallel and perpendicular to the focal strip are presented. These results are compared with calculated data using reported energy distribution of backscattered electrons (E.H.Darlington, J. Phys. 8 (1975) 85). The integrated heat flux associated with backscattered electron is experimentally measured and compared with calculated values for incident power of 86 kW. With 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 be higher for high incident power densities and for targets of high atomic numbers and can be used in pre-coating treatments of substrate such as outgassing and cleaning, keeping it at elevated temperature during continuous coating process, and also for outgassing, cleaning and sharing heat load required for pre-melting of the feeder material during melting and casting.