Quality evaluation of CsI photocathodes for the ALICE/HMPID detector

The facility for the production of the large area (64×42cm2) CsI photocathodes for the ALICE/HMPID detector has been equipped with a photo-current scanner system for the in situ measurement of the CsI response over the full photosensitive area before transfer to the detector. The photo-current measured on a first batch of 17 PCs, out of the 42 needed to fully equip the seven HMPID modules, has been correlated with test beam measurements in order to define acceptance criteria. Furthermore the system's sensitivity to variations in quantum efficiency allows us to study various effects such as post-deposition heat enhancement or decreased quality due to ageing.