Preliminary Assessment of Thermal Noise in the Radiative Heat Exchanger for Low-Frequency Applications in the Einstein Telescope Integration internship

Abstract

The Einstein Telescope, which will be one of the third generation gravitational wave detectors, will open a new window in our understanding of the universe by allowing the examination of many astrophysical phenomena thanks to its high sensitivity. In order to achieve this high resolution, it is of great importance to minimize noise sources, especially thermal noise. In this context, the design of gravitational wave telescope mirrors to operate in cryogenic conditions plays a critical role in reducing the noise in question.

Within the scope of this master's thesis, radiative heat exchangers developed to enable the mirrors to reach cryogenic temperatures were examined. The first cooling test carried out at the Liege Space Center was successfully completed and the reduction of the temperature of the mirror to 22 Kelvin was an important milestone.

However, considering that these developed systems not only cool the mirrors but also could be a potential source of thermal noise, this effect was also investigated in detail. In this context, heat exchangers were first modeled as systems with a single degree of freedom, then as systems with multiple degrees of freedom. The thermal noise power spectral density values of the mirrors were calculated numerically.

At the end of the study, the total heat exchanger induced thermal noise values of the mirrors were determined depending on the frequency range. Knowing the thermal noise occurring in this frequency range allows us to distinguish the noise components originating from the telescope's own structure, thus contributing to the increase in measurement precision.