Pushing towards the ET sensitivity using 'conventional' technology

TL;DR

The paper investigates whether conventional technologies can reach the Einstein Telescope's ambitious sensitivity by reconfiguring a Advanced LIGO–like interferometer to a 10 km arm length and stepwise improving key noise sources. Using the GWINC noise model as a baseline, it demonstrates a plausible sequence of conventional enhancements—longer arms, tuned signal recycling, higher input power, quantum-noise suppression, larger beam sizes, cryogenic cooling, advanced suspensions, underground operation, and heavier optics—to approach the ET target. The authors conclude that, in principle, conventional tech could suffice, except for gravity-gradient noise at low frequencies which would require non-conventional suppression, underscoring the need to explore alternative topologies and the associated cost–feasibility trade-offs. They provide detailed parameter changes and inspiral-range estimates to serve as a reference for future feasibility studies.

Abstract

Recently, the design study `Einstein gravitational wave Telescope' (ET) has been funded within the European FP7 framework. The ambitious goal of this project is to provide a conceptual design of a detector with a hundred times better sensitivity than currently operating instruments. It is expected that this will require the development and implementation of new technologies, which go beyond the concepts employed for the first and second detector generations. However, it is a very interesting and educational exercise to imagine a Michelson interferometer in which conventional technologies have been pushed to - or maybe beyond - their limits to reach the envisaged sensitivity for the Einstein Telescope. In this document we present a first sketchy analysis of what modifications and improvements are necessary to go, step-by-step, from second generation gravitational wave detectors to the Einstein Telescope.

Figures (3)

• Figure 1: Originally proposed target sensitivity of the Einstein Telescope (blue) from Michele. For comparison a rough estimate of the average sensitivity of first (red) and second generation (also called 'advanced') gravitational wave detectors (green) are included.
• Figure 2: Fundamental noise contributions to the sensitivity of a potential advanced detector (blue solid line). The solid red line is an approximation of the ET design target (blue line from Figure \ref{['fig:target']}). Please note that every noise source is at least at some frequencies above the ET design target, thus we have to improve every single noise contribution to guarantee compatibility with the targeted ET sensitivity.
• Figure 3: Result from the analysis presented in this document. With the changes suggested above we can roughly achieve (black solid line) the ET design target (red solid line) only using conventional technology. However, in the end it should be possible to further increase the peak sensitivity by simultaneously improving shot noise, coating Brownian noise and residual gas pressure.