  COMPASS is a fixed target experiment at CERN SPS aimed to study Hadron
Structure and Spectroscopy. Hadron Identification in the momentum range between
3 and 55 GeV/c is provided by a large gaseous Ring Imaging Cherenkov Counter
(RICH-1). To cope with the challenges imposed by the new physics program of
COMPASS, RICH-1 have been upgraded by replacing four MWPCs based photon
detectors with newly developed MPGD based photon detectors. The architecture of
the novel detectors is a hybrid combination of two layers of THGEMs and a
MicroMegas. The top of the first THGEM is coated with CsI acting as a
reflective photo-cathode. The anode is segmented in pads capacitively coupled
to the APV-25 based readout. The new hybrid detectors have been commissioned
during 2016 COMPASS data taking and stably operated during 2017 run. In this
paper all aspects of the novel photon detectors for COMPASS RICH-1 are
discussed.
