A Modular Readout Electronics for Multi-Wire Proportional Chambers with Individual Channel Readout

We present a modular readout system for the new curved 3He-detectors built for the upcoming powder diffractometer ErwiN at the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), Germany and the upgrade of the cold powder diffractometer DMC at the Paul Scherrer Institut (PSI), Switzerland. These detectors are based on multi-wire proportional chambers (MWPC) with individual readout of all cathode wires and stripes. Nine individual curved MWPC segments are mounted inside a 3He-filled common pressure vessel to form a homogenous, seamless detection area. The modular design of the detector is mirrored by the architecture of the readout electronics. This permits to adapt the readout system to similar detector types with an arbitrary number of MWPC segments. The analog Front-end consists of charge sensitive preamplifiers with 350 ns peaking time followed by comparators to deliver a Time-over-Threshold (ToT) signal. The ToT-signals are encoded and timestamped at 80 MHz by an FPGA-based board directly mounted on top of each MWPC segment. The signal processing includes a cluster recognition in x- and y-position as well as in signal arrival time. The neutron impact position is then determined using a centre-of-gravity algorithm based on the ToT-information. A further FPGA-based board gathers and post-processes data from all the segments for reconstructing neutron events occurring at the boundary of two adjacent segments. Finally, the reconstructed events are delivered to the DAQ system with 10-bit position resolution, timestamping with 100 ns precision and total charge deposit with 8-bit resolution.