The first test on a magnetically focused mirror corrector

Abstract

In some recent publications we have discussed the possibility of correcting both spherical and chromatic aberrations using a magnetically focused mirror. If such a scheme could be made to work it would represent the simplest possible type of aberration corrector and for this reason we decided to test the principles of operation using a simple experimental system (Fig. 1). Electrons are obtained from a TFE source operating at 3.6kv which is immersed in a region of uniform magnetic field which refocuses them at a point 5 cm away. At this position we placed a simple specimen consisting of a copper grid with a holey plastic film. Electrons which pass through a hole in the specimen enter a region where the magnetic field is supplemented by a uniform electrostatic field which can act as a mirror. By a proper adjustment of the strength of this field the electrons can be refocused on the reverse side of the specimen where the total aberration should be zero.