電子衝撃加熱型電子銃内の衝撃電子軌道

Abstract

An electron-heated point cathode gun has been studied for the development of a high brightness gun with a long cathode life. Only the tip part of the tungsten point cathode is heated by the electron bombardment. The temperature of the cathode tip can be raised even up to the melting point. The bombarding electrons are produced from a loop filament of an annular gun which is set inside the Wehnelt electrode of the point cathode gun. One of the most important factors of this gun is the heating efficiency of the point cathode. In order to make clear the dependence of the heating efficiency on various factors, we have carried out the numerical calculation of the bombarding electron trajectories in the plane which includes the loop filament and intersects perpendicularly the optical axis of the point cathode gun. It has been found that the bombarding position and angle on the point cathode depend on the initial energy and angular spreads of the electrons emitted from the loop filament as well as the magnetic field generated by the heating current of the loop filament. The heating current of the loop filament has been found to be a dominant factor affecting the heating efficiency, so that the use of a reasonably thin loop filament is desirable for the further improvement of this gun.