Electron Accelerator for a 1-MeV Electron Microscope

Abstract

Highly stabilized electron accelerators are required for the supply of high energy microscopes, such as the 1-MeV microscope installed by RCA at the Research Center of the US Steel Corporation at Monroeville, Pa. As shown in figure 1, the accelerating voltage is generated by a 5-stage Cockcroft-Walton cascade rectifier with an additional filter stack. The accelerator structure is connected to the cascade generator through a high-ohmic damping resistor which also serves as a filter resistor in connection with the capacitive part of the precision voltage divider in parallel to the accelerating tube. The beam tube consists of porcelain isolators sealed together by metal flanges and double 0 rings. The accelerating electrodes are made of highly polished mumetal as well as the cylindrical shields which cover the accelerating gaps. Entire mumetal screening is necessary to minimize the effect of the magnetic field of the earth on the electron beam. The beam tube is surrounded by several insulating cylinders which include the voltage divider, a bleeder-chain, a coupling capacitor for the compensation of the residual ripple voltage, and six insulating shafts which are used to control the electron gun and the injector system at high voltage potential.