The amount of material in the beam was minimized in order to reduce the contamination with fragments resulting from photonuclear disintegration or inelastic nuclear collisions of the projectile. For the same reason, any beam counter or vacuum window that could not be removed, was made of the lowest Z material possible.
The beam position and focus are monitored with filament scanners which provide beam profiles in the vertical and horizontal directions during beam tuning. They are moved out of the beam during data taking. The beam spot has a diameter of about 1 mm. The ion beam is selected upstream of the target by two counters in coincidence, S1 and T0, which define the beam direction and position within the experiment.
S1 and T0 are quartz Cherenkov counter which identify the beam particle species by the emitted Cherenkov light. Thus it can reject the beam contamination. For both S1 and T0 an electronic discriminator window is set in order to select only beam particles, rejecting beam fragments and pileup. Any interaction in the S1 counter or in the remaining gas of the beam pipe is rejected by a set of two veto counters, V0 and V1, in anticoincidence with S1 and T0. These are ring shaped scintillating counters centered on the beam. The innermost, V0, is placed inside the beam pipe and has a hole of 1 cm diameter. The dimensions and positions of all elements in the beam line is summarized in the Beamline document.