Abstract
The ion-optical configurations of the narrowest image width are examined in the case of two homogeneous magnetic fields by numerical calculations. The image width W is a function consists of 10 variables which characterize each field and 8 constants which represent the system dimensions and ion beam properties. Particularly, the free-space distances between two magnetic fields d and the one between the second magnetic field and the image l″ are determined by the double focusing conditions, where a practical point of view for the construction is considered.
The functional behavior of W, d and l″ are investigated as a function of 10 variables. It is clarified that the function W has sharply pointed minima for all variables, and that there are many cases that the increse of W at minima with the change of some variable is compensated by the change of another variable. This compensating property is also the case for d and l″.
Based upon these facts, it is possible to decide a suitable configuration realizing an image of width about 0.2 micron with easier construction and adjustment.
