Problem description:

An electron  injector. Problem  is modelled  as axysimmetric
electrostatic  system   consisting  of  cathode,  anode  and
focusing electrode.  Cathode is  semi-spheric, the  focusing
electrode is  semi-spheric with  an opening  near the  axis,
anode is a flat disk with an opening in the centre.


Model geometry:

     Cathode radius = 0.005m;
     Focusing electrode radius = 0.015m;
     Tube radius = 0.035m;
     Focusing electrode and anode inner radii = 0.005m.

     Distance between centres of electrodes = 0.05m.

Voltages:

     Cathode = 200V;
     Focusing electrode = -40V,
     Anode = 10000V.

Problem is axysimmetric.