Evaporation takes place under vacuum, typically 10E-5 or deeper. A current (5 to 10 kV) is sent through a tungsten filament and heats it to the point where thermionic emission of electrons takes place. The filament is located in an area outside the deposition zone, in order to avoid contamination. The electrons are focused and directed toward the evaporant by means of permanent magnets or electromagnets. As the electron beam hits the surface of the evaporant, the kinetic energy of its motion is transformed to heat via the impact.