  A dual-phase xenon time-projection chamber was built at Nikhef in Amsterdam
as a direct dark matter detection R&D facility. In this paper, the setup is
presented and 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 $\sigma_E/E$ is
(5.8 $\pm$ 0.2)% at an energy of 511 keV. This was achieved using a combination
of the scintillation and the ionization signals. A photomultiplier tube gain
calibration technique, based on the electroluminescence signals occurring from
isolated electrons, is presented and its advantages and limitations are
discussed.
