THGEM-based photon detectors for the upgrade of COMPASS RICH-1

The RICH-1 detector of the COMPASS Experiment at CERN SPS is undergoing an important upgrade: four new Photon Detectors, based on MPGD technology and covering a total active area larger than 1.4 m2 will replace the MWPC-based photon detectors in order to cope with the challenging efficiency and stability requirements of the new COMPASS measurements. The new detector architecture consists in a hybrid MPGD combination: two layers of THGEMs, the first of which also acts as a reflective photocathode as it is coted with a CsI film, are coupled to a bulk Micromegas on a pad segmented anode; the signals are read-out via capacitive coupling by analog F-E based on the APV-25 chip. These detectors are the first application in an experiment of MPGD-based single photon detectors. All aspects of the COMPASS RICH-1 Photon Detectors upgrade are presented and large emphasis is dedicated to the engineering aspects, the mass production and the quality assessment of the MPGD components. The status of the detector commissioning is also presented.