Use of triplet quadrupole magnets for symmetric focusing of the electron beam

Dear André

Thank you very much for your response. First of all, could you please explain to me how can I make the picture you attached?

Now I try to focus the beam with thin lenses (increasing the field strength), but still keep the asymmetry of the beam at the focal point position.

Also, I could not understand the following results that I got in the case of a single lens with a 1 cm thickness and beam rms is 30 mm (attached plot). We can see that the asymmetry of the beam is still maintained at the focus point position, although I expected the beam to focus in one plane and defocus in another plane.
1_RMS-10mm_BeamTEST_2D_Y01_01mm

Please, could you take a look at your instinct and help me figure this out?

focus_Q5.flair (17.7 KB)
focus_Q5.inp (20.9 KB)
Q1Q3magfld.f (3.8 KB)

Best regards
Zohrab