| 摘要 |
PROBLEM TO BE SOLVED: To provide a device and a method capable of optimally setting bias voltage of an electron gun without requiring complicated operation. SOLUTION: On the method of controlling emission current from a filament of the electron gun provided with a plurality of resistors arranged between the filament and a Wehnelt electrode having resistance values different from each other, a setting, for dividing a range of acceleration voltage into the same number of areas as that of the resistors, is accepted, and the resistors are switched so that one having a resistance value corresponding to the size of the area of acceleration voltage can be used to the area of the acceleration voltage. COPYRIGHT: (C)2007,JPO&INPIT
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