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Description
The Einstein Telescope (ET) requires 120 km of beam pipes with a diameter of 1 meter. Additionally, to achieve the ET's design sensitivity, a residual pressure of below $10^{-10}$ mbar must be attained. Meeting both requirements will cause the vacuum system cost to represent one-third of the total anticipated budget, given current production and vacuum technologies. Continuous on-site manufacturing of the beam pipes in the tunnels, along with the adoption of novel cleaning methods, can lower costs. Laser cleaning is proposed to clean ferritic stainless steel surfaces and remove adsorbed water, eliminating the need for high-temperature and time-consuming bakeout. Therefore, controlling moisture re-adsorption is crucial. This work investigates how the humidity of the nitrogen purge influences water‑vapor re‑adsorption on cleaned surfaces, with the aim of identifying a humidity level that keeps water contamination within acceptable limits. A gas humidity control system is designed to regulate the water concentration in the purging gas. The system is connected to a vacuum chamber to measure the effects of water re-adsorption.