Future liquid-xenon (LXe) based observatories for rare processes, such as XLZD, require testing of large components and sub-assemblies in cryogenic liquid or gaseous xenon environments. Here we present results from the stable operation of a shallow dual-phase LXe TPC with an inner diameter of 133.4\,cm and a height of 3.1\,cm in the unshielded PANCAKE platform, without underground suppression of cosmic-ray backgrounds. A total of 340\,kg of xenon was used in the experiment, of which 127\,kg constituted the active TPC mass. Measurements of the LXe purity-dependent electron lifetime and the electron drift velocity in LXe demonstrate that sensitive measurements to characterize the TPC performance are possible in a high-background environment, even with a very basic PMT-based light detection system. Improving this will straightforwardly reduce the TPC threshold, which was observed to be around 15\,keV for electronic recoils in TPC operation.
@article{arxiv.2601.15938,
title = {Operating a large-diameter dual-phase liquid xenon TPC in the unshielded PANCAKE facility},
author = {Julia Müller and Jaron Grigat and Robin Glade-Beucke and Sebastian Lindemann and Tiffany Luce and Gnanesh Chandra Madduri and Jens Reininghaus and Marc Schumann and Adam Softley-Brown and Andrew Stevens},
journal= {arXiv preprint arXiv:2601.15938},
year = {2026}
}