| 摘要 |
PURPOSE:To enable an electron gun to be used stably for a long period of time by enclosing the circumference of a cathode tip with a protective cover except for its electron ejector part and removing adverse effects due to evaporative substances of a heating element and a cathode tip. CONSTITUTION:Between the front ends of a pair of supporting electric poles 11, 12 is arranged an LaB6 cathode tip 14 which is inserted in a heating element 13 composed of, for example, pyrolytic graphite, and both the heating element 13 and the cathode tip 14 are fixed tightly by the force of screws. The protective cover 15 is made of ceramics like alumina, zirconium dioxide, etc. which are anticorrosive at high temperature, low in vapor pressure and excellent in insulation. The front end part of the cathode tip 14 is inserted into a through hole 15b, the upper part of the heating element 13 is covered by a main cover 15a, and moreover the heating element 13 and the sides of the cathode tip 14 are covered by sides 15c, 15d and fixed to the supporting electric poles 11, 12 with screws. |
