PURPOSE: To prevent a change of protruding length of a needle-shaped electrode during use by providing a throttle part in the inside of a suppressor electrode and a positioning fixing groove so that an insulating material of fixing the needle-shaped electrode by fastening fixed parts is pressed to this throttle part.
CONSTITUTION: A tungsten needle electrode 1 of <100> axial azimuth providing a coating layer composed of Zr and oxygen in the surface is fixedly welded to a tungsten wire 2 for supporting this electrode heated. This wire 2 is fixedly welded to also a metal strut fixed through an electric insulating material 6. A position fixing throttle part 5 is provided in the inside of a suppressor electrode 6, and the insulating material 6 is brought into contact with the throttle part 5 through a spacer 7 of thickness necessary for obtaining a proper protruding length of the electrode 1. A position fixing groove 8 is provided on a side surface of the insulating material 6, and when fastened a fixed part 9 mounted on an electrode 3, the insulating material 6 is fixed in a manner pressed to the throttle part 5.
TERUI YOSHINORI
IDE MASARU
