A high-pressure gas TPC prototype with hybrid charge-optical readout

A high-pressure gas Time Projection Chamber (TPC) with optical readout and a hydrogen-rich gas mixture has the potential to provide the most precise measurement of neutrino interactions on nuclei. An R&D study for developing such a prototype could inform the design of a highly capable near detector for future neutrino experiments like DUNE. The Warwick TPC (WarTPC) serves as an R&D platform for readout technology and gas mixture development in high-pressure gas TPCs. It features a hybrid charge and optical readout, utilizing a TimePix3 camera for optical detection and two Thick Gas Electron Multipliers (THGEMs) for charge and light amplification. We have conducted measurements with various argon-CH₄ mixtures at 1 bar and with pure argon at pressures up to 6 bar. In this report, we present the prototype and discuss the observed effects of CH₄ quenching on argon VUV scintillation light, as well as the suppression of VUV light production at high pressures.