A dual tunnel structure for the Einstein Telescope

Abstract

We present a novel tunnel architecture for the Einstein Telescope that departs from the traditional large-cavern approach and reduces the excavated volume by an order of magnitude. In the proposed design, seismic isolation systems are housed in raise-bore wells extending upward from the main tunnel toward an upper service tunnel. The preisolators for the most sensitive optics are located in the service tunnel, supported directly on strong rock, whereas the other filters are distributed along the wells within compact, side-access vacuum chambers. Shorter, separate wells accommodate the seismic isolation systems for less demanding optics. This configuration provides substantial advantages: easier lock acquisition and improved robustness of the interferometers, lower-frequency pendulum stages, reduced congestion around the test masses, simplified installation and maintenance, improved vacuum partitioning, strong physical decoupling between the high- and low-frequency interferometers, and compatibility with advanced sensors for Newtonian-noise cancellation.