| 摘要 |
<p>PURPOSE:To extend the life of a heater in an electron gun of such a type as to heat a cathode with radiant heat. CONSTITUTION:A bottomed cylindrical cover 8 is fitted to a cathode from its electron-emitting surface side. As a material for the cover, a high melting point metal having a lower emissivity than a material for the cathode 6 is used. For example, in the case that LaB6 is used for the cathode, tantalum and molybdenum are used for the cover. A hole 8a for fitting of an electron emitting part 6a of a cathode is formed in the center part of the bottom of the cover. Consequently, since the cathode surface except the electron emitting part 6a and a heating surface 6b is covered with a material having a lower emissivity than that of the cathode, the apparent radiant heat of the cathode can e reduced. As a result, the temperature of the heater for heating the cathode can be decreased and thus the life of the heater is extended.</p> |
