The construction of the Baikal-GVD neutrino telescope is motivated by its discovery potential in astrophysics, cosmology and particle physics. Its primary goal is the detailed study the diffuse flux of high-energy cosmic neutrinos and the search for their sources. It will also search for dark matter candidates (WIMPs), for neutrinos from the decay of super heavy particles, for magnetic monopoles and other exotic particles. It will also be a platform for environmental studies in Lake Baikal. The reference scientific communities are a) high energy neutrino astrophysicists joined in the global neutrino network, with the projects IceCube (South Pole, operating), ANTARES (operating) and KM3NeT (under construction, both Mediterranean See) and Baikal-GVD (Lake Baikal, under construction, first 3 clusters operating); b) astrophysicists using other messengers: charged cosmic rays, optical and radio waves, X-rays, gamma-rays and gravitational waves, c) particle physicists, d) limnologists.
The detector will utilize the deep water of Lake Baikal instrumented with optical modules (OMs) – pressure resistant glass spheres with large photo-multiplier tubes (PMTs). The PMTs record the Cherenkov radiation from secondary particles produced in interactions of high-energy neutrinos inside or near the instrumented volume. From the arrival times of light at the PMTs and from the amount of light, direction and energy of the incoming neutrinos are derived. The Infrastructure will consist of a network of autonomous subdetectors – so-called clusters – each of them with 288 optical modules. A cluster comprises eight vertical strings attached to the lake floor: seven side strings on a radius of 60 m around a central one. Each string carries 36 OMs, arranged at depths between 735 and 1260 meters (instrumented length: 525 m). The vertical spacing between the OMs along a string is 15 m. The OMs are functionally combined in 3sections. A section comprises 12 OMs with data processing and communication electronics and forms a detection unit (DU) of the array. All analogue signals from the PMTs are digitized and processed in the sections and are sent to shore if certain trigger conditions (e.g. a minimum number of fired PMTs) are fulfilled. The clusters are connected to shore (3.5 km distance) via a network of cables for electrical power and high-bandwidth data communication. The shore station provides power, detector control and readout, computing resources and a high-bandwidth internet connection to the data repositories. The overall design allows for a flexible and cost-effective implementation of the Research Infrastructure. The large detection volume, combined with high angular and energy resolutions and moderate background conditions in fresh lake water allows for efficient study of cosmic neutrinos, muons from charged cosmic rays and exotic particles. It is also an attractive platform for environmental studies.
Baikal-GVD is rooted in the long-term operation of its predecessor NT200. During the Design Study (2008–2010) the basic elements of GVD – new optical modules (OMs), FADC readout units, underwater communications and trigger systems – have been developed, produced and tested in-situ. During the Preparatory Phase (2011–2015), comprehensive in-situ tests of all elements and systems of the future detector as part of several engineering arrays have been performed. The Preparation phase was concluded in 2015 with the deployment of a demonstration cluster comprising 192 OMs. The construction of the first phase of Baikal GVD (GVD-I) was started in 2016 by deployment of the first cluster in its baseline configuration, consisting of 288 OMs arranged at eight 525 m long strings. The array was upgraded by the deployments of the second GVD cluster in April 2017 and of the third GVD cluster in April 2018. Commissioning of GVD-I (8 clusters, volume 0.4 km3) is envisaged for 2020. The second stage GVD-II with 14 clusters will be completed by 2023.