Operating large size GEM detectors using a novel optocoupler based biasing scheme for the Muon Chamber system of CBM experiment

An assembly of large area (∼2000 cm2) triple GEM detector modules will be used for the first two stations of Muon Chamber (MUCH) system of Compressed Baryonic Matter (CBM) experiment at FAIR. Each GEM foil has its top surface segmented into 24 divisions. A novel HV distribution schematic has been implemented to power the individual segments. This design based on optocouplers is not only cost-effective but also has the capability to isolate the faulty segments if required, during the process of data taking. A large size prototype based on this layout was designed and fabricated. The performance of such a prototype has been discussed. Radiation and stability tests of the optocouplers with regards to CBM requirements (a ten-year integrated dose of ∼1012neq/cm2 for neutrons and ∼30 krad for Gammas) has been reported.