Downstream of the object box, the beam is only a few nA, compared to several µA upstream of it. The beam then passes through a collimator to eliminate the particles scattered a long way from the beam’s optical axis and thus to limit the aberrations induced by the focusing system: the final intensity is 1000 to 15,000 particles per second, depending on the collimator used.
After this second collimation, the beam passes through a focusing system consisting of four magnetic quadrupole lenses, coupled to ensure the ion beam is focused symmetrically. This system can achieve a theoretical enlargement factor of around 1/20, i.e. the beam obtained under vacuum after focusing is approximately 20 times smaller than the object collimator used.
An electrostatic deflector, placed upstream on the line, can cut the beam in a few microseconds after a given time on the target or, coupled with an ion detection system, when the required number of particles has reached the target.
Just before its extraction in air, an electrostatic displacement system is used to precisely position the beam on the target. This system can move the ion beam from one point to another in a few microseconds, and can thus generate different irradiation patterns (single point, grid, cross, etc.).