Beam optics of the soft-landing deceleration stage
In the soft-landing set-up, the 50 kV ions are slowed down by simply applying
a suitable potential to the target
(actually, the entire set-up is put on high voltage!).
The ions are kept focused on their destination by using an array of
five electrostatic lenses.
The target potential is derived from the ion source potential
to ensure a well-defined potential difference.
The ion optics are strongly influenced by the geometry close to the target.
Optimal results could be obtained by designing the target
together with He-flow crysostat
such that a completly flat target is obtained.
It turned out to be necessary to mount a diafragm just in front of the target
in order to go to extremely low energies.
Ion trajectories together with the electrostatic field lines
as obtained from program SIMION.
Since this program is unable to handle space charge effects,
the current density should be considered to be vanishingly small.