Electron beam source assembly

摘要

An electron beam source assembly includes a water cooled crucible positioned substantially flush with the top of the block. A magnet is attached to each long sides of the rectangular block to establish parallel opposed pole magnets with the crucible therebetween. A smaller magnet is attached to each end of each longitudinal magnet to form a second and a third parallel magnet pair. The six magnets produce plano-convex magnetic field lines above the crucible, and additional plano-convex field lines of increased field strength extending outwardly from the end of the block having the four magnets. A magnetic base plate provides a low reluctance path to decrease magnetic flux at the crucible. An electron gun emitter mechanism is sheltered from vapors formed at the crucible and includes architecture to enable electrons to be freely emitted from the filament, without being subjected to the magnetic field lines from the magnet pairs, in a direct path outwardly through an open cavity and through a window formed in the end of the electron source assembly. The freely emitted electron beam assumes a trajectory passing solely through plano-convex magnetic field lines to produce an inverted image at the crucible that is substantially a one-to-one mapping of the filament.