xmpl2d12, 12th 'example' data file for CPO2D

Simulation of the space-charge repulsion of a mixed beam of electrons and carbon ions.


The set-up is almost the same as in example file xmpl2d11.dat, except that the beam is a mixture of electrons and positively charged carbon ions.

The following data were obtained when the memory and speed of PC's was much more limited than at present, so the available number of segments was small and the requested inaccuracies were fairly high to give a quick demonstration.


There are 6 electron rays and 6 ion rays (see the relevant note), all directed towards the point (r,z) = (0,0). Each ray is given a current proportional to the area of the annulus from which it starts.

The electrons are given an energy 1 eV, an atomic mass number 0.0005486 (=1/1822.9) and a charge number -1, while the carbon ions are given an energy 12*1822.9 eV, a mass number 12 and a charge number +1. The electrons and ions therefore have the same velocity. The ray currents are the same for the carbon ions and the electrons. The combined space charge should therefore be zero, and both types of particle should travel in straight lines. This behaviour is accurately reproduced.

As another test of the 'variable mass' option described in the relevant note, delete the 6 ion rays. The space-charge repulsion in the electron beam will then be similar to that obtained with the example file xmpl2d11.dat.


As a test of the 'constant mass' option, use the same initial ray conditions given in xmpl2d11.dat, but replace the line that starts with 'va' by a line that starts with 'co' and follow it with the line '1.0 12.0' -see the relevant note. Also scale down the currents by the square root of the mass -that is, divide them by sqrt(12*1822.9). The shape of the beam will then be similar to that obtained with the example file xmpl2d11.dat.