Improvements & Performance of the Hitachi 200KV Electron Microscope

Abstract

1.Electron gun - A new high voltage cable and porcelain insulator has been developed. A successful study of superior surface treatment of the insulator and improved means of sealing the cable resulted in eliminating surface discharge of the insulator. Since an electrode discharge and surface discharge of an insulator cannot be completely eliminated in a vacuum of the order of 10-5 to 10-6 torr, an high capacity vacuum system is employed to assure high vacuum and a discharge free system. Further, small quantities of inert gases such as N2, Ar, He etc. is introduced into the gun chamber to maintain a vacuum of 1 to 2 x 10-4 torr.2.Evacuating system.At 200KV it is necessary in a single stage electron gun to provide greater insulating distance to inhibit discharges. Consequently, the electron gun chamber is inevitably larger. The gun chamber volume of this electron microscope is 32 liter. A 4″ diameter single manifold and 1200 liter/sec. oil diffusion pump comprise the evacuating system.