vacuum systems / energy demand / metal / metal fume bubbles / applied filler metal / molten metal round / residual gas molecules / energy entry / minimum energy input / filler metal / metal-arc welding processes / gas-shielded narrow gap welding process / metal-working industry / steel materials / molten metal groove melting pool welding direction / metal vapour cavity / kinetic energy / material processing / molten metal / particular applications / energy conversion / low-voltage technology / fluid metal / electron beam technology / high energy density / manufacturing high welding speed / energy / horizontal beam manipulation systems / /