Advanced Virgo: a 2nd generation interferometric gravitational wave detector (1408.3978v3)

Abstract: Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network with the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detections of gravitational waves and to opening a new observation window on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction.

• The paper presents Advanced Virgo’s enhanced sensitivity design that increases the observable universe’s volume by a factor of 1000.
• It employs a dual-recycled interferometer with high-power lasers and heavier mirrors to suppress various noise sources.
• The phased operational upgrades and advanced cryogenic systems significantly improve gravitational wave detection for astrophysical events.

Overview of the Advanced Virgo Detector

The paper "Advanced Virgo: a second-generation interferometric gravitational wave detector" provides a comprehensive overview of the development and expected performance of the Advanced Virgo (AdV) interferometer. As an evolution of the initial Virgo detector, AdV aims to significantly enhance the sensitivity to gravitational waves (GWs), increasing the volume of space that can be observed by a factor of 1000. This improvement arises from multiple technological advancements designed to suppress various noise sources and improve the overall system performance.

Key Technological Improvements

Advanced Virgo incorporates a myriad of technical enhancements over its predecessor:

1. Interferometer Optical Configuration: AdV will employ a dual-recycled interferometer setup. This includes a signal-recycling cavity alongside the traditional power-recycling cavity, providing the ability to tune the shape of the sensitivity curve to optimize detection of different astrophysical sources.
2. Laser System: To achieve greater sensitivity at high frequencies, the system relies on a laser with higher power, delivering up to 200 W of power after the input mode cleaner. This system is supported by thermal compensation to manage heat-induced optical aberrations effectively.
3. Mirrors and Optics: The test masses are heavier (42 kg compared to the previous 21 kg) to counteract radiation pressure fluctuations. The optical components, including the beam splitter and compensation plates, are designed with ultra-low absorption fused silica and sophisticated polishing methods to reduce thermal noise.
4. Stray Light Control: New diaphragm baffles and seismic isolation for photodiodes minimize the impact of scattered light, enhancing the signal-to-noise ratio of the detector.
5. Advanced Cryogenics and Vacuum Systems: The cryotraps at the ends of the interferometer arms reduce residual gas pressures, thereby suppressing noise generated by fluctuations in the refractive index due to gas molecules.

Sensitivity Goals and Expected Outputs

The target sensitivity for Advanced Virgo is designed to significantly outperform that of its predecessor. The system intends to achieve a sensitivity allowing the detection of coalescing binary neutron stars at distances of approximately 140 Mpc and binary black holes at up to 1 Gpc. Achieving these targets involves tuning several system parameters, such as laser power and signal-recycling cavity settings.

Progress and Future Directions

Since the release of the Technical Design Report, ongoing developments have refined the detector’s mechanical and optical systems. For instance, new models have been adopted to better project suspension thermal noise and gravity gradient noise against the background of observed seismic activity at the Virgo site.

The paper outlines a strategic timeline extending into the future, with stages of early and late operations planned to incrementally increase the capability of the detector. This phased approach facilitates the integration of complex systems and offers periods dedicated to commissioning and data-taking.

Implications and Speculations

The enhancements presented in Advanced Virgo signify a critical step forward in the international effort to open a new window of gravitational-wave astronomy. The detection capabilities of AdV will be integral to gaining insights into the violent and dynamic universe, improving our understanding of phenomena such as black hole mergers and neutron star collisions.

Conclusion

Advanced Virgo demonstrates significant technological progress aimed at enhancing the detection of gravitational waves. This paper provides crucial insights into the design, construction, and expected performance of the detector, heralding a new era of empirical astronomical research. The development of AdV plays a pivotal role in the joint observatory network, which includes Advanced LIGO and GEO HF, aiming for real-time detection and multi-messenger astronomy efforts.