http://www.twi.co.uk/j32k/protected/band_3/ksas001.html
"Electron Beam Welding (EBW) is a fusion process for joining metals which uses a highly focused beam of electrons as a heat source. Usually the electrons are extracted from a hot cathode, accelerated by a high potential - typically 30,000-200,000 volts, and magnetically focused into a spot with a power density of the order of 30,000 W/mm 2 . This causes almost instantaneous local melting and vaporisation of the workpiece material. The electron beam is thus able to establish a 'keyhole' delivering heat, deep into the material being welded. This produces a characteristically narrow, near parallel, fusion zone allowing plain abutting edges to be welded in a single pass for material thicknesses ranging from less than 0.1mm to greater than 200mm."
" It is also possible to project high power electron beams into the atmosphere and produce single pass welds in steel in thicknesses of more that 40mm, but the weld width is typically greater than welds made in vacuum."
