Large resistive 2D Micromegas with genetic multiplexing and some imaging applications

The performance of the first large resistive Micromegas detectors with 2D readout and genetic multiplexing is presented. These detectors have a 50×50cm2 active area and are equipped with 1024 strips both in X- and Y-directions. The same genetic multiplexing pattern is applied on both coordinates, resulting in the compression of signals on 2×61 readout channels. Four such detectors have been built at CERN, and extensively tested with cosmics. The resistive strip film allows for very high gain operation, compensating for the charge spread on the 2 dimensions as well as the S/N loss due to the huge, 1 nF input capacitance. This film also creates a significantly different signal shape in the X- and Y-coordinates due to the charge evacuation along the resistive strips. All in all a detection efficiency above 95% is achieved with a 1 cm drift gap. Though not yet optimal, the measured 300 µm spatial resolution allows for very precise imaging in the field of muon tomography, and some applications of these detectors are presented.