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Description
Many state-of-the-art optical readout micro-patterned gaseous detectors (MPGDs) are equipped with of standard Gas Electron Multipliers (GEMs), which are 50 μm thick. The COBRA_125, a 125 μm thick, triple-electrode MPGD has the potential to further increase the optical gain of these detectors: whereas in a GEM, the Electroluminescence light is only produced in the holes, the two independent stripped electrodes imprinted on the bottom face of the COBRA_125 define a second high-field region that produces additional light. Furthermore, the increased thickness of the COBRA_125 adds electrical robustness, meaning that higher voltages can be applied across the holes before the onset of microdischarges.
In this work, we compare the absolute light yield of He-CF4 mixtures produced by a 125 μm COBRA to the one obtained with a standard GEM (50 μm thick). The detector, operated in flow-mode, was irradiated with X-rays from a 55Fe source. A Large Area Avalanche Photodiode (LAAPD) was used to readout the light produced by the COBRA_125 and by a standard GEM. Our results show that the COBRA_125 is able to increase the light yield of a standard GEM by an order of magnitude, proving to be a strong solution for future optical MPGDs.
