| 摘要 |
PROBLEM TO BE SOLVED: To make the shape of the end of electron beam able to the trimmed and make mitigable the variation of extraction electrode by reducing temperature difference caused near the end of the extraction electrode. SOLUTION: The electron source 6a is composed of a hot cathode 8 generating electron 10 in surface shape and two extraction electrodes extracting generated with it as an electron beam 10a and is provided with an upstream side first extraction electrode 12 and a downstream side second extraction electrode 14 with the same electric potential as it. In between the first extraction electrode 12 and the second extraction electrode 14, masks 26 shielding the end region of the electron 10 in surface shape from the hot cathode 8 and shaping the end parts of the electron beam 10a extracted out of the second extraction electrode 14 are provided at both ends in Y-direction of the second extraction electrode 14. Each of the masks 26 consists of porous conductor and electrically insulated from other conductor and is in floating potential state.
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