| 摘要 |
PURPOSE:To prevent securely the deterioration of voltageproof property owing to a rise of temperature of an insulator which supports a central conductor, by avoiding the heating of the central conductor which fixes and holds the electron beam source, owing to the heat of the electron beam source. CONSTITUTION:When a cathode 5 is heated by a power source 12 to radiate electron beams, the heat is liable to transmit to a central conductor 8 through a shield electrode 6 as it was conventionally. However, the shield electrode 6 in not connected to the end of the central conductor 8, different from the conventional one, but fixed and held at a fixing tube 15, and the end of the fixing tube 15 is opened inside a vacuum container 1. Since the inside of the central conductor 8 is vacuum, the heat is not liable to radiate to the central conductor 8, even though the heat is transmitted to the fixing tube 15. And even though the heat is transmitted to the fixing tube 15, its transmission to the central conductor 8 is remarkably reduced, because the fixing tube 15 is composed of a low thermal conductive material such as stainless steel, and because the fixing tube 15 and the central conductor 8 are connected through a thermal insulator 16.
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