Design of an experimental setup for continuous positronium beam formation via Ps− production and laser photo-detachment

QUPLAS is an experiment designed to measure the gravitational acceleration of positronium (Ps) using an interferometric phase-shift technique that requires a continuous-wave, low-divergence beam with tightly controlled phase-space properties. To meet these requirements, the project develops a two-step beam-formation scheme based on the production of negative positronium ions (Ps−) and their laser photo-detachment to generate neutral Ps while preserving beam quality. This paper reports the experimental results that validate the key enabling subsystems: the photoelectric characterization of a Na covered W converter used to identify and reproduce surface conditions associated with enhanced performance of Ps− formation, and the realization and characterization of a high-power optical cavity for photo-detachment, demonstrating stable high circulating power and cavity parameters consistent with design expectations. Together, these results establish a concrete technological basis for integrating the source and photo-detachment stages into the full QUPLAS beamline and for producing the beam conditions required for precision positronium interferometry and gravity measurements.