Speaker
Description
The E-TEST prototype is designed to address key technology challenges for the Einstein Telescope, centred on a 70 kg mono-crystalline silicon test mass cooled to 20–25 K via radiative cooling. The setup provides direct access to the thermal noise and mechanical dissipation regimes relevant to ET's cryogenic operation.
The mechanical quality factor is measured using a non-contact electrostatic drive (ESD), allowing continuous, real-time monitoring via constant-amplitude resonant excitation, with improved stability over conventional ring-down methods. Measurements are performed as a function of temperature, with particular attention to the anisotropic mechanical losses in mono-crystalline silicon, governed by crystal orientation, fabrication processes, impurity content etc.
Thermal characterisation of the test mass and its coupling to the suspension is carried out in parallel, covering heat extraction, temperature stability, and spatial gradients during cool-down. A laser-based optical readout probes bulk temperature and gradients in situ, while laser absorption is studied through its influence on resonance frequency and dissipation during cooldown. These experimental results will be interpreted alongside ESD multiphysics simulations and LAMMPS-based phonon modelling, informed by XRD, FTIR spectroscopy, and birefringence characterisation of the silicon material, collectively providing a more accurate computational description of mechanical loss mechanisms.
The discussion presented here contributes to a deeper understanding of thermal noise in cryogenic silicon test masses and supports the optimisation of suspension, actuation, and thermal management strategies for future gravitational-wave detectors.