With an electrode system, mounted in the collision chamber we can distinguish between different types of charged particles. See Measurements.
Scheme of the electrode system in the collision chamber: parallel to the beam.
Both the collector c and the repeller r, forming together a condenser-like measuring system, are surrounded by guardplates p and q, put at the same voltage as respectively c and r. The special shape of the guard plates perpendicular to the beam direction avoids secondary ionization processes that might be caused by possible slow electrons created in the interaction region by following closed trajectories perpendicular to the electric and magnetic fields. In front of both plates two grids g1 and g2 are mounted. Around the collision chamber there is a coil m, which can produce a magnetic field of 300 Gauss in the interaction region.
It was checked that all electric and magnetic fields were strong enough to cause saturation of the measured currents.