| 摘要 |
<p>PURPOSE:To obtain always a single beam inspite of a shallow bias between a cathode and a Wehnelt electrode by contracting the point side of the cathode to a small diameter and assigning roughness of a plane of said point to a specific mesh. CONSTITUTION:A single crystal cathode 10 such as LaB6 is formed by contracting the point side of a square pole 11 to a small diameter, while the point of a conical part 12 there of is surface-processed in the direction orthogonally crossing the direction of electron emitting. Further the roughness of 1-10 meshes is formed on said surface-processed point plane part 13 and a Wehnelt electrode as well as an anode are arranged above the point of the cathode 10. Through said constitution, electrons emitted from the point plane part 13 appear as one big spot without splitting so that a single beam can be obtained inspite of low heating temperature and a shallow Wehnelt bias.</p> |
