The neutrino telescope IceCube in Antarctica has established the new discipline of neutrino astronomy with landmark observations. To fully exploit the potential of the observatory, the international collaboration behind IceCube plans  a major extension of the detector that is frozen underground into the eternal ice of the South Pole.  A white paper submitted to the Journal of Physics G outlines the need for and design of IceCube-Gen2, the next-generation extension of IceCube. By adding new optical and radio instruments to the existing detector, IceCube-Gen2 will increase the annual rate of cosmic neutrino observations by an order of magnitude, and its sensitivity to point sources will increase to five-times that of IceCube.

“With ten years of data from IceCube, we see first evidence for sources of high-energy, cosmic neutrinos, and thus have a new view of the most energetic processes and objects in the universe,” says Marek Kowalski, IceCube-Gen2 coordinator, based at DESY. “Only the tip of the iceberg is visible but it’s very encouraging. With IceCube-Gen2, we want to fully open the window to neutrino astronomy by increasing the rate of discoveries by an order of magnitude, and clarify the role of the highest-energy processes shaping our Universe.”

Projected to be completed in 2033 with construction costs around 300 million euros, IceCube-Gen2 is a major endeavor. The first step is already underway with the IceCube Upgrade, funded by the U.S. National Science Foundation NSF and also by the Helmholtz Association, which will add seven strings with new and enhanced optical modules to DeepCore, the center of the IceCube array. The next phase will be to add 120 additional strings, which will be spaced about 240 meters apart in a sunflower-like pattern around IceCube that is designed to encompass a large volume while avoiding “corridors” through which misleading signals may pass. The new digital optical modules, or DOMs, which should be able to collect nearly three times as many photons as current IceCube DOMs, will be spaced 16 meters apart on the string, between 1.3 and 2.6 kilometers below the surface, resulting in a total detector volume of nearly eight cubic kilometers.

“Over the past 30 years we have seen the exciting evolution of neutrino observations, from first neutrino detections using early instruments deployed deep in glacial ice sheets to the long-sought discovery of high-energy astrophysical neutrinos with IceCube,” says Darren Grant of Michigan State University, spokesperson for the current IceCube Collaboration. “IceCube-Gen2 represents the timely opportunity to build on existing expertise and technological advances to move from the discovery era to precision neutrino astronomy.”

Near the surface, IceCube-Gen2 will have a new radio component made up of detector “stations” covering an area of approximately 500 square kilometers. Each station consists of three strings holding radio antennas that will be deployed close to the surface of the ice. This array will detect radio emission generated in the ice by particle showers, allowing scientists to reconstruct the energy of the shower and arrival direction of the neutrino. “With the collaboration embracing the radio technique as a complementary tool to target the very highest energies, I look forward to finding many ‘firsts’ in this uncharted territory,” says radio detector specialist Anna Nelles from DESY.

From a global perspective, IceCube-Gen2 will transform the multimessenger astrophysics landscape; once built, the extended detector will join a network of other large-scale observatories that survey the sky in gamma rays, gravitational waves, and cosmic rays. IceCube-Gen2 is designed to address some of the mysteries that persist in neutrino and multimessenger astronomy. Specifically, the extension will allow to resolve the high-energy neutrino sky at energies higher than ever before (energies up to EeV, or 10¹⁸ eV), investigate cosmic particle acceleration through multimessenger observations, reveal the sources and propagation of the highest energy particles in the universe, and probe fundamental physics with high-energy neutrinos. These advancements would shape the next era of multimessenger astronomy and revolutionize our understanding of the high-energy universe.

“Neutrinos are but a recent addition to the palette of tools that help us explore the cosmos,” says Olga Botner, head of the IceCube group at Uppsala University in Sweden. “While IceCube opened a new window onto the distant, violent universe, with IceCube-Gen2 we will look further, with more precision and over a larger energy range. IceCube-Gen2 will play an essential role in the era of multimessenger astronomy, paving the way for new, groundbreaking discoveries.”

The collaboration already knows that IceCube-Gen2 is logistically possible. The construction of IceCube that currently consists of 86 strings carrying 5160 DOMs demonstrated the ability to build and deploy instruments on time and on budget in an Antarctic glacier at the South Pole—one of the most inhospitable environments on the planet. While there will be logistics challenges in such a large project, the collaboration is prepared to meet them, always taking into account that South Pole is hosting a multitude of scientific projects with their own logistical needs.  

“Publishing a white paper is an important milestone for every future research project,” says Markus Ackermann, head of the IceCube group at DESY. “With this document, we want to share our enthusiasm about the scientific potential of IceCube-Gen2 with the broader scientific community and outline a path toward the realization of this exciting project.”

 

Reference: 
IceCube-Gen2: The Window to the Extreme Universe; The IceCube-Gen2 Collaboration: M. G. Aartsen et al. Submitted to the Journal of Physics G; https://arxiv.org/abs/2008.04323