| 摘要 |
<p>PURPOSE:To steeply reduce the number of times for cleaning a Wehnelt cylinder by using either a boride, tantalum, chrome or 40% nickel steel as material for a control electrode. CONSTITUTION:A Wehnelt cylinder is formed using either tantalum, chrome, or 40% nickel steel having such a thermal expansion ratio as is close to that of LaB6 that is emitter material. By so doing, it is possible not only to reduce the number of times necessary for cleaning the Wehnelt cylinder to a large extent but also make such cleaning unnecessary.</p> |
