| 摘要 |
PURPOSE:To improve magnification and aberration of a multistage accelerating tube by providing a changeover mechanism of number of stages such as a switch to ground the potential of each stage successively in the linkage with acceleration voltage. CONSTITUTION:A switch box 33 is so designed as to ground the potential of each stage from the lowest to upper stages successively by the switching action of the switch SW. When the acceleration voltage of a multistage accelerating tube is to be lowered, output voltage Va of an acceleration voltage source 3 is not change but in the switch box 33 a terminal (t)3 drawn out from a proper voltage dividing point is grounded. Thereby, a good ion probe can be obtained even when the device is operated at a low acceleration voltage.
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