Commissioning of dual-phase xenon TPCs with PMT gain calibration using scintillation light

A dual-phase xenon time-projection chamber was built at Nikhef in Amsterdam as a direct dark matter detection Ru0026D facility. In this paper, the first results from a calibration with a $^{22}$Na gamma-ray source are presented. The results show an average light yield of (5.6 $pm$ 0.3) photoelectrons/keV (calculated to 122 keV and zero field) and an electron lifetime of (429 $pm$ 26) $mu$s. The best energy resolution, using both the scintillation and the ionization signals, is (5.8 $pm$ 0.2) %. A photomultiplier tube gain calibration technique, based on the electroluminescence signals occurring from isolated electrons, is presented and its advantages and limitations are discussed.