| 摘要 |
<p>PURPOSE:To make it possible to easily make adjustment to recover any shift of the center of a negative electrode in relation to a wehnelt electrode, by means of a negative electrode mounting base set up in such a way as capable of moving freely in a plane perpendicular to the axis of a holder on which the wehnelt electrode is fixed through screw mechanism. CONSTITUTION:Wehnelt electrode 3 engaging with its holder 7 via a screw mechanism around the external circumference of its end, is provided, around its side surface near the bottom, with a dial 11 sectioning the circumference at an equal interval. In one side area of the holder 7, is fixed an index panel 12 made of a transparent plate etc. and provided with a datum line in its center, while confronting the dial 11. On the other hand, base 4 holding the negative electrode and incorporated into the internal space of holder 7 is arranged in such a way as being freely shifted on the plane perpendicular to the holder axis, while touching the step formed on the inside wall of holder 7. Thus, position adjustment can be made with extremely high accuracy and also quickly between the negative electrode and wehnelt electrode 3.</p> |
