We report on the design, construction, commissioning, and performance of a threshold gas v{C}erenkov counter in an open configuration, which operates in a high luminosity environment and produces a high photo-electron yield. Part of a unique open geometry detector package known as the Big Electron Telescope Array, this v{C}erenkov counter served to identify scattered electrons and reject produced pions in an inclusive scattering experiment known as the Spin Asymmetries of the Nucleon Experiment E07-003 at the Thomas Jefferson National Accelerator Facility (TJNAF) also known as Jefferson Lab. The experiment consisted of a measurement of double spin asymmetries $A_{parallel}$ and $A_{perp}$ of a polarized electron beam impinging on a polarized ammonia target. The v{C}erenkov counters performance is characterised by a yield of about 20 photoelectrons per electron or positron track. Thanks to this large number of photoelectrons per track, the v{C}erenkov counter had enough resolution to identify electron-positron pairs from the conversion of photons resulting mainly from $pi^0$ decays.
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