xmpl3d96, 96th 'example' data file for CPO3D

Automatic iteration to optimise a focus, using the option to maximise

the current within a given circle.

Based on xmpl3d06.dat, using the same geometry.

The number of segments used in the present example is small, for a quick demonstration.

The present data differ from those in xmpl3d06 in the following ways:

(1) Voltage number 2 is initially 5.85.

(2) The 'cylindrical beam' option is used, with 15 randomly distributed ray directions. The total current is 8 mA, so that the current in the minimum sector is 1 mA, which is therefore the maximum current that can be in the focus spot.

(3) A new (May 2013) option is used to maximise the current that is within a circle of radius 0.006 mm, centred at the centre of the test plane. The option is set to select the best 13 of the 15 rays, allowing 2 rays to lie at any distance outside the given circle. A second radius of 0.008 mm is specified so that rays lying at distances between 0.006 and 0.008 are weighted linearly (that is they are given weights of 1.0 and 0.0 at distances of 0.006 and 0.008 respectively, and linearly between those limits). If the second radius is not used in this example, where there is a small number of rays that all carry the same current, then the minimisation procedure becomes non-smooth and terminates prematurely.

It can be seen that the final value of v2 is 5.844, and that the 'max current' is 0.711 mA. In fact it can be seen from the xy view that 8 rays have distances less than 0.006, 4 are between 0.006 and 0.008, 1 is just outside 0.008 and the remaining 2 are further away.

In a more serious study of this lens the cylinders would obviously be given many more subdivisions, there would be a larger number of rays and more iterations of the voltages would be used. It would be particularly important to subdivide the cylinders finely near the gaps between the cylinders, either by using iterative subdivision (adaptive segmentation) , as described in file xmpl3d04.dat, or by treating each cylinder as a series of shorter touching cylinders, the outer ones of which have the smallest subdivisions.