On 19/11/2018:

During the target ladder calibration (see elog entry #41) we also replaced the collimator (thickness ~24mm, diameter 3mm) located immediately upstream from the target ladder - that is between the upstream and central sections of the chamber. We mounted an aluminium collimator (thickness ~1mm, diameter 5mm). See attached picture 1.

Using the same telescopic sight as that used for the target ladder calibration, we aligned the 5mm collimator with the beam axis.