The Einstein Telescope will become part of the major European research infrastructure. There are now two competing initiatives for an underground location. In addition to Sardinia (It), this is the border area of the Netherlands, Belgium and Germany. This is suitable for an underground observatory because the soft top soil blocks vibrations caused by human activity on the surface, so that the measurements are not disturbed. It will be decided in 2025/2026 where the Einstein Telescope will be located and construction should start around 2030. A large number of universities and scientific institutions from the Netherlands, Belgium and Germany are now working on a joint candidacy.
Measuring gravitational waves
Measurements of gravitational waves by existing observatories and the new Einstein Telescope take place with laser beams. These are sent into long corridors in two directions and reflected at the ends by mirrors; at the starting point they are captured by a detector. The measuring signal depends on the difference in the distance traveled by the two laser beams. A passing gravity wave influences that path length difference and therefore the measuring signal. Scientists obtain information from this about the event that was responsible for the gravitational wave in question.
New technologies needed
To make the Einstein Telescope ten times more accurate than existing observatories, new technologies are needed. These are developed, among other things, in the special R&D lab ETpathfinder in Maastricht (NL), which was opened three years ago. To finance the research, the R&D scheme was established as part of the ET valorization program with a financial contribution from the Dutch National Growth Fund. The scheme has five calls; the first was for vibration-free cooling, which is necessary to make the measurements much more accurate.
Twente research into vibration-free cooling
At the University of Twente (UT) in Enschede (NL), research into vibration-free cooling based on sorption technology that works with activated carbon has been taking place for twenty years. This takes place in the Energy, Materials & Systems (EMS) department under the leadership of Professor Marcel ter Brake. Demcon kryoz from Enschede has further developed, based on the cooling principle, a prototype cryogenic microcooler from the department into a product. Cooll from Hengelo (Ov, NL) is working on the opposite process, heating based on the same technology. The company has also set up a factory for the production of activated carbon. Thus, the three Twente parties cover the complete chain for vibration-free cooling: fundamental research, equipment and process development and production of the compressor material.
Three-stage cooling system
The three joined forces for the Einstein Telescope last year when the call for the R&D scheme was opened. Last month it was announced that their proposal had been accepted. The Twente consortium will receive an amount of 2.6 million euros for a period of three years to make the technology suitable for the Einstein Telescope. They will develop a three-stage cooling system that works with three different coolants: neon, hydrogen and helium. The cooling process starts at -203 °C (70 Kelvin), the temperature reached with the liquid nitrogen. Two intermediate steps are required to reach the final, most difficult step to -263 °C (10 Kelvin): the coldest point in the cooling system. Ultimately, they will build three copies of the cooling system, one for research at the UT in Enschede and two for the ETpathfinder in Maastricht.
Scaling up
Pieter Lerou, managing director of Demcon kryoz, was in charge of the proposal submission: “The principle for vibration-free cooling is known and we have made it work on an industrial scale. But that was with a microcooler, while the coolers for the Einstein Telescope work with an immense compressor and a much higher power. Much fundamental research is still required for this upscaling. For this, we use our knowledge of cryogenic technology and our experience in designing, modeling and building high-tech cooling systems. We also contribute our systems engineering expertise. We ensure that all knowledge and expertise and all required components come together and that the end result is a reliably functioning system that is delivered according to plan and within budget. This is certainly necessary, because with the outcome of our project we will contribute to the bid book for the Dutch-Belgian-German location of the Einstein Telescope.”
University of Twente
“For UT, and the Department of EMS in particular, this is a fantastic project,” says Associate Professor Michiel van Limbeek. “We focus in our projects on the development of technology for concrete applications. For us, these are often in the field of energy and sustainability, but also in the field of Big Science with projects for CERN, ESA, and very concretely also for the Einstein Telescope. An ambitious project in which technology that we have been working on for a long time will now actually be applied. It takes the technology another step further towards broader applications in the market where there is a demand for vibration-free cooling.”
High-quality activated carbon
Johannes Burger, founder of Cooll: “For home heating, Cooll has developed a thermally driven heat pump that works with high-quality activated carbon. Compared to an HR boiler, this technology ensures a saving of 30-40% on (green) gas consumption in homes. Our technology is a direct spin-off from the development of vibration-free cryogenic sorption coolers at the UT; twenty years ago, we were partly responsible for this. The discovery of an activated carbon with very high-quality properties made both applications possible. In recent years, Cooll has further developed this material together with an American partner for use in our heat pump technology and made it suitable for production. We are pleased that we can supply the unit cells for the vibration-free compressor as a new spin-off from our development. This completes the circle. We are also happy to make our knowledge of compressor technology available for the project.”
Milestone
Program manager Jorg van der Meij (LIOF): “With this grant, we celebrate a milestone in the Einstein Telescope valorization program, now that a consortium of visionary companies and a leading knowledge institution has received the first R&D subsidy. Their innovative plans around vibration-free cooling not only strengthen the candidacy for the Einstein Telescope, but are also promising for other sectors and applications.”
Collaboration with knowledge institutions and companies
Robbert Dijkgraaf, outgoing Minister of Education, Culture and Science, thinks it is fantastic to see that companies are working to develop the technology for the Einstein Telescope. “This collaboration between knowledge institutions and companies shows how joining forces can lead to groundbreaking research and innovation. The Einstein Telescope promises not only new scientific discoveries, but also economic growth and employment. Although we are not yet sure where the telescope will be located, this collaboration is an important investment in our country and international science.”
Man on the Moon project
Pieter Lerou from Demcon kryoz is of course proud of winning the project. “With this challenging Man on the Moon project, we are building on our country’s cryogenic legacy. It started with Leiden professor Heike Kamerlingh Onnes, who managed to liquefy helium in 1908 and received the Nobel Prize for this in 1913. He laid the foundation for a flourishing cryogenics industry in our country. Several Dutch companies, including Cryoworld and Stirling Cryogenics, are involved with the project as associate partners. Our research will help in the development and realization of vibration-free cryogenic cooling systems for other high-tech applications, such as electron microscopy and space instrumentation.”