The reasons that caused these phenomena are less concentrated hot spots and less intense electromagnetic focusing effect, as shown in Figures 14(c) and 14(g) and Figures 15(c) and 15(g).
Images in Figure 17(d) exhibit the electromagnetic focusing in the center of samples in Group 3.
Thus, the electromagnetic focusing along the axis is mainly caused by the microwave refracted from the cambered surface, and only within the penetration depth region near end surfaces may microwave refraction from two end surfaces have an effect on the microwave superposition.
It was long recognized the resolution of TEMs was limited by intrinsic imperfections in the devices electromagnetic focusing
lenses, commonly referred to as spherical aberrations.
In fact, it is an extension of the classic electromagnetic focusing
problem in which one wants to determine the features of a source capable of radiating a field focused in a given target direction in free space.
and alignment coils, located below the anode, provide the beam focus and alignment capability needed to ensure that the high velocity stream of electrons being produced passes cleanly through the series of in-line orifices it encounters in traversing the succession of progressively increasing pressure stages.