PURPOSE: To radiate a uniform electron beam flux and to prevent an insulating support structure from being contaminated with a sublimate of LaB6 by a structure where a part of an LaB6 thermoelectron radiator other than an electron- radiating face is buried in a graphite heating element.
CONSTITUTION: A heating element 20 is composed of one graphite block; a thermoelectron radiator 21 composed of LaB6 is fit and inserted into a bottomed hole 22 in the heating element 20; that is to say, an elongated part united with the top part is buried in the heating element 20. Accordingly, it is possible to use a slender LaB6 with a diameter of, e.g., 300μm. In this case, a face at the surface of the heating element 20 and at an electron-radiating face of the LaB6 thermoelectron radiator 21 may be a plane or can be a curved surface having a radius ot curvature. Even in either of these faces, only the electron- radiating face of the LaB6 thermoelectron radiator 21 is exposed from the graphite radiator 20. Thereby, it is possible to prevent an insulating support from being contaminated.
NISHIMURA ISAO
DAIKYO YOSHIHISA
YASUDA HIROSHI
