BoNus: Development and use of a radial TPC using cylindrical GEMs

A specialized system of target and detector was developed at Jefferson Lab to provide new access to information about neutron structure from electron-neutron interactions. It allows identification and measurement of spectator protons produced in e-d→e-psX scattering events. The detector is a radial time-projection chamber optimized for the acceptance of low-momentum protons. Gas gain is provided by three cascaded curved Gas Electron Multipliers (GEMs), the first application of GEMs in any configuration other than flat. This article provides details about the development and construction of the detector, its performance, and the analysis of the data from the successful running of its first physics experiment.