For precise and uninterrupted measurements at extremely low temperatures, the Einstein Telescope (ET) requires vibration-free cooling. The consortium, consisting of Demcon kryoz, the University of Twente, and Cooll, is developing a solution based on sorption cooling, a principle already used in cryogenic microcoolers. The consortium is currently building vibration-free macro-format coolers, a technology that has never before been applied on this scale for cryogenic applications. With this development, the consortium is creating a unique value proposition in vibration-free cryocooler technology.
Vibration-Free Cooling for ET
The Einstein Telescope will measure gravitational waves caused by gigantic cosmic events deep in the early universe. Due to the immense astronomical distances involved, these waves reach Earth as only minute ripples. Such signals can only be measured at extremely low temperatures and in complete silence. Conventional cooling systems disrupt this silence, for example through the vibrations generated by a refrigerator compressor. Developing vibration-free cooling is therefore one of the major challenges for the consortium, which is working on a sorption-cooling-based solution together with research partner the University of Twente and ETpathfinder. The Einstein Telescope Lab at Maastricht University, established on the initiative of Nikhef, serves as the location where the technology is being validated and integrated for ET applications.
Scorption Cooling from Micro to Macro
Cooling is a cyclic process in which a cooling medium, such as a gas, removes heat from a target location and releases it elsewhere. In conventional closed-cycle cooling systems, gas compression is achieved using moving components driven by a motor. These moving parts generate vibrations, which are highly undesirable for ET applications.
Sorption cooling works through the adsorption and desorption of gas by activated carbon. During the compression phase, gas is adsorbed by the carbon, causing pressure to decrease; during desorption, pressure builds up, driving the cooling process. The entire cycle is powered by heat and contains no moving parts.
Since 1995, the University of Twente has conducted research into sorption cooling, leading to several successful spin-off companies. One of these is Demcon kryoz, which develops cryogenic Joule-Thomson microcoolers for a wide range of applications, from microscopes to communication satellites. This expertise led to the company's involvement in ET and its role as consortium leader of the Zero-Vibration Sorption Cryocooler project.
Challenging questions drive upgrades with broad impact
“At Demcon, we are accustomed to carrying out R&D for customers who come to us with complex challenges, and we enjoy tackling them,” says Project Manager Adrie Visser. “In a big science project such as ET, those challenges are even greater because of the extremely low vibration and temperature requirements. The scientific standards are exceptionally high. Being able to work on such projects motivates us to keep improving. A concrete example is the LEM toolboxes we use in projects. LEM, a specialty of Demcon kryoz, is a lumped-element modelling method for analysing complex systems. For simulations and analyses, we use models that have been under continuous development at the University of Twente since 1995. To meet ET’s demanding requirements, we have further expanded these toolboxes. What makes this unique is that we can simulate an entire system dynamically within a single model.”
Ready for integration in laboratory enviroments
The consortium began scaling up the sorption cooling technology and has already achieved several important milestones, says Romaine Kunst, Thermal System Engineer at Demcon kryoz. “Our first milestone was the design report from the conceptual phase, which was positively received by ETpathfinder last year.”
“With our systems engineering approach, we conducted this preliminary phase with exceptional thoroughness. This enabled us to provide our partners with all relevant information, including a risk analysis and studies on how our system will perform in combination with the other ET systems. We have now nearly reached the milestone of being ‘ready for integration’.”
At present, work is focused on the most important component of the cooling system: the sorption compressor,” Visser explains. “Together with the University of Twente, Demcon and Nikhef, we are assembling the first systems. We expect to complete full integration of one system in the High Pressure Lab at the University of Twente this summer. If the results are positive, we will begin parallel activities in the cleanroom in Maastricht. By the end of the year, we expect to have the first fully integrated system ready for ETpathfinder.”
Testing in Twente, integration in Maastricht
A sorption cryocooler will first be assembled and tested in Twente. Kunst explains: “In Maastricht, all activities take place in a cleanroom environment, which is essential for the ultra-high vacuum (UHV) conditions in which the Einstein Telescope will operate. For the initial test campaigns at the University of Twente, the environmental requirements are less stringent, providing more flexibility to experiment in the laboratory. Using additional sensors, we will validate the vibration performance of the cryocooler. The key question is whether the system is sufficiently vibration-free and whether it meets the most important requirement: not amplifying the background noise measured at 32 nanometres peak-to-peak in Maastricht. Once the measurements in Twente have been successfully completed, integration of the sorption cryocooler into the ET test setup in Maastricht can begin.”
Partners in cooling technology and expertise
The successful progress of the project is largely the result of strong collaboration between the consortium partners. Cooll, also a spin-off of the University of Twente, delivered the sorption compressor cells earlier this year, complete with activated carbon pellets for gas adsorption. Kunst explains: “Cooll is the only company in the world capable of manufacturing these cooling cells with such a large internal surface area, making them highly efficient. For the special cryogenic application within the Einstein Telescope, significant effort was invested in optimising the design and performing lifetime testing. As a result, we are confident that the cooling cells will operate reliably for at least ten years. Before this project, that work formed part of an intensive R&D trajectory that also generated knowledge applicable to other customers and applications.”
For ET, the sorption cryocoolers form part of an efficient three-stage cooling process that starts at the temperature of liquid nitrogen. In addition, a dedicated pre-cooling system prepares the cryocooler before operation. Stirling Cryogenics supplied the specialised cryogenic pumps, CryoFans, while Demaco installed the complete liquid nitrogen infrastructure at the University of Twente and Maastricht University facilities. Additional expertise was provided by partners such as ASTRON, the Netherlands Institute for Radio Astronomy, particularly in the field of black heat-absorbing coatings.
Strengthening the Dutch Cryogenic Ecosystem
According to Visser, suppliers across the Netherlands have been inspired by this pioneering project. “We were looking for components that had to be compatible with both ultra-high vacuum and cryogenic environments. That combination is extremely rare, which led us to engage with a wide range of suppliers. In one case, a supplier even questioned whether its UHV components would remain suitable under cryogenic conditions. We connected that supplier with the University of Twente to carry out the necessary testing.”
Kunst adds: “One supplier of the heaters used in the sorption compressors initially recommended a lower power level than we required. We therefore performed our own calculations to verify that the higher power level could be used safely. Especially during the detailed design phase, finding suppliers capable of meeting all requirements proved challenging. Ultimately, the project has advanced the Dutch cryogenic network not only technically, but also in terms of knowledge sharing and collaboration.”
Specialist in Systems Engineering
A key partner in the project is Nikhef, Kunst continues. “They are the end user of our system and, together with Maastricht University, lead the ETpathfinder laboratory. Our system has 21 interfaces with other systems in the lab. Ensuring seamless integration therefore required extensive coordination with Nikhef.”
Albert van Dorssen, Business Developer at the Einstein Telescope Valorisation team, sees systems engineering as a crucial factor in the project's success: “From the very start, Demcon kryoz adopted a rigorous approach to defining and evaluating all requirements and interfaces. This expertise helps ensure that the development of highly advanced scientific infrastructure, with its strong research focus and eventual industrial application, progresses smoothly.”
Kunst adds: “At the start of the project, I prepared a Customer Requirements Document for Nikhef, including a complete overview of all 21 interfaces. Because these requirements were clearly documented from the beginning, we could continuously refer back to them throughout the project, preventing major obstacles later on.”
According to Visser, this explains why Demcon kryoz, despite being a relatively small company supported by the larger Demcon organisation, can play a connecting role within a consortium of partners such as Nikhef and the University of Twente. “This works because each partner contributes its specific expertise. Nikhef has its own laboratory and extensive specialist knowledge, while the same applies to the University of Twente. Our role is to maintain the overall system perspective, ensure that all interfaces fit together both functionally and physically, and as project manager make sure that all parties collaborate effectively.”
Looking Ahead to New Applications
“The final result is a unique cooling system,” says Kunst. “It represents a major step forward compared with existing cooling technologies.” Such improvements could also be highly relevant for telescopes, where optical systems are still often cooled using mechanically driven compressors that can negatively affect image resolution. “For me personally, it is a dream to continue developing this technology. Space applications and astronomy are obvious fields of interest, but there are many other research applications where improved resolution can make a difference. Examples include medical imaging systems for cooled samples and advanced scientific microscopes.”
Quantum computing is another promising area, where vibration requirements are even more stringent and operating temperatures are even lower. “Our system also offers the advantage of being fully closed,” Kunst explains. “Many systems still rely on externally supplied liquid nitrogen for cooling.”
Van Dorssen adds: “The compact size of sorption cryocoolers is especially attractive for the construction sector. Across many industries, there is growing demand for cooling solutions that are both smaller and more robust.”
Visser concludes: “The right stakeholders are paying close attention to what we are achieving for the Einstein Telescope. And it is not only within Demcon kryoz that people are already imagining new applications for this technology.”
Valorisation of Unique Sorption Cooling Technology
This groundbreaking sorption cooling technology offers numerous opportunities for valorisation in new scientific and industrial applications. To explore these opportunities, the consortium partners welcome contact with interested parties, who can reach out to Albert van Dorssen, Business Developer within the Einstein Telescope Valorisation team: Team Valorisation - Einstein Telescope for Business.