Reaching ultra-high vacuum for a large vacuum vessel in an underground environment

¹ LP2N, Laboratoire Photonique, Numérique et Nanosciences, Université Bordeaux–IOGS– CNRS:UMR 5298, rue F. Mitterrand, F–33400 Talence, France
² Dipartimento di Fisica e Astronomia, Università di Bologna, Via Berti-Pichat 6/2, I-40126 Bologna, Italy
³ LNE–SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 61, avenue de l’Observatoire, F–75014 Paris, France
⁴ LSBB, Laboratoire Souterrain à Bas Bruit, CNRS UAR3538, Avignon University - La grande combe, 84400 Rustrel, France

^* e-mail: benjamin.canuel@institutoptique.fr

Abstract

Located far from anthropical disturbances and with low seismic and magnetic background noise profiles, the LSBB facility is the ideal location for a new hybrid detector for the study of space-time strain. The MIGA infrastructure [1], utilizes an array of atom interferometers manipulated by the same beam, the resonant optical field of a 150 m long optical cavity. The infrastructure constitutes a new method for geophysics, for the characterization of spatial and temporal variations of the local gravity, and is a demonstrator for future decihertz gravitational wave observation. Such an infrastructure requires ultra-high vacuum (10⁻⁹ mbar) on a size (150 m) and scale (36 m³) not typically seen in underground laboratories other than CERN [2], and especially in underground environments with high humidity (up to 100%) and significant dust contamination (milimetric to micrometric porous rock particles). Here, we detail the status of the MIGA infrastructure and describe the ongoing generation and analysis of the vacuum works - this comes from tests of the prototype vacuum vessel, focusing on heating cycles, residual gas and heating analysis.