| 摘要 |
A plurality of electron gun assemblies having transverse magnetic fields to focus an electron beam into a crucible to vaporize a material may be closely placed in parallel by inserting between the assemblies a thin magnetic fence magnetized across its surfaces. The polarity of a fence surface is the same as the polarity of the adjacent sidewall magnet forming the transverse field so that the opposition will prevent magnetic flux from passing between adjacent assemblies and a resulting distortion and defocusing of the electron beam.
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